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A risk of waiting: the weekly incidence of hypertensive disorders and associated maternal and neonatal morbidity in low-risk term pregnancies

American Journal of Obstetrics and Gynecology, Volume 214, Issue 3, March 2016, Pages 389.e1 - 389.e12

Background

Elective induction of labor (eIOL) prior to 39 weeks’ gestation is discouraged because of presumed fetal benefits. However, few data exist on the maternal risks of expectant management. To date, no study has evaluated the maternal risk of developing a hypertensive disorder of pregnancy with expectant management of a low-risk gravid at term.

Objective

We sought to evaluate the development of hypertensive disorders in term low-risk expectantly managed patients.

Study Design

This is a retrospective cross-sectional study from 19 US hospitals, from 2002 to 2008 (Safe Labor Consortium) including all nonanomalous, cephalic, singleton pregnancies at 37–41 weeks. Women with a history of hypertension, diabetes mellitus, cardiovascular disease, or planned cesarean delivery or from centers with incomplete hypertensive data were excluded. Women with eIOL in each week were compared with women managed expectantly until the next week of gestation or beyond. The primary outcome was the frequency of hypertensive complications.

Results

Of 114,651 low-risk deliveries, 12,772 (11.1%) had eIOL. The cohort was 49.2% nulliparous, 51.1% white, and obese (mean body mass index 30.2 kg/m2). The risk of developing any hypertension in expectantly managed women was 4.1% after 37 weeks, 3.5% after 38 weeks, 3.2% after 39 weeks, and 2.6% after 40 weeks. Compared with eIOL, women with hypertensive disorders had significantly higher rates of cesarean delivery and maternal morbidities (intensive care unit admission or death, third- or fourth-degree lacerations, maternal infections, and bleeding complications) at each week of gestation and the composite neonatal morbidity at 38 and 39 weeks of gestation.

Conclusion

For women at low risk expectantly managed at term, there is a risk of developing hypertensive complications for each additional week of pregnancy, with associated increases in maternal and neonatal morbidities.

Key words: elective induction of labor, expectant management, hypertensive disorders of pregnancy.

Based on previous studies examining neonatal outcomes and their relationship to gestational age, elective induction of labor (eIOL) prior to 39 weeks’ gestation is discouraged because of concerns for neonatal morbidity.1 and 2 However, more recent publications have sought to examine maternal, fetal, and neonatal outcomes by comparing induction at different stages to the real-world obstetric condition of expectant management. These works have shown that expectant management of pregnancies at term is not without risk including, increased fetal deaths, increased cesarean delivery, and neonatal and maternal morbidities.3, 4, 5, 6, 7, 8, and 9 One maternal morbidity of expectant management about which less has been written is the spectrum of pregnancy-related hypertensive disease and the cumulative risks associated with its occurrence.

Worldwide, hypertension is a leading cause of maternal mortality and is associated with significant obstetric morbidity10 and fetal death.11 Eclampsia, preeclampsia, and gestational hypertension are unique to pregnancy and are defined by new-onset blood pressure elevation after 20 weeks’ gestation.12 and 13 Hypertensive disorders of pregnancy complicate approximately 3–10% of all pregnancies10, 14, 15, and 16 and account for 12–16% of maternal deaths in developed countries.17 The overall incidence of hypertensive disorders in pregnancy has been increasing, partially attributed to the rise in obesity and comorbidities in pregnancy.18

As we, using this data set,6 and others, with vital statistics data sets,3, 4, 5, 7, 8, and 9 have previously shown, eIOL in women at low risk has been associated with a decreased risk of several obstetric complications including postpartum hemorrhage,3 chorioamnionitis,6, 7, and 8 obstetrical laceration,8 and 9 and operative delivery.3, 6, 7, 8, and 9 Because women with eIOL are, at the onset, devoid of hypertensive complications by definition, the elective induction of patients at low risk could also confer a benefit of avoiding the development of obstetric-related hypertensive morbidity and its associated maternal and fetal morbidity/mortality.

To date, no study has evaluated the maternal risk of developing a hypertensive disorder of pregnancy with expectant management of a gravid at low risk at term. Therefore, we sought to describe the incidence of hypertensive disorders of pregnancy in expectantly managed pregnant women at low risk at term.

Materials and Methods

Study population

We selected our study cohort from the database of the Consortium on Safe Labor, a study conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health.19 In brief, this was a retrospective, cross-sectional study involving deliveries from 2002 through 2008 from 12 clinical centers and 19 hospitals representing 9 American College of Obstetricians and Gynecologists (ACOG) districts. The population was then standardized by assigning a weight to each subject using ACOG district, maternal race/ethnicity, parity, and plurality based on 2004 national data.19 and 20 Institutional review board approval was obtained for this analysis.

The Figure presents the flow diagram for our cohort selection, as originally described in the paper by Gibson et al6 comparing expectantly managed term pregnancies with electively induced deliveries. Briefly, from the initial data set of all deliveries (n = 233,736), we limited the group to singleton term pregnancies of 37 to 42 weeks’ gestational age in vertex presentation (n = 155,848) in the Consortium on Safe Labor Dataset.

gr1

Figure Flow diagram of cohort selection and distribution of subjects by week of pregnancyThe selection of our low-risk term cohort and the distribution of our final cohort into those electively induced or expectantly managed by week of pregnancy.HIV, human immunodeficiency virus.Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

To limit confounding, we excluded all those with a prior uterine scar or planned (elective) cesarean delivery (n = 136,014). We also excluded those with fetal anomalies, women who had more than 1 pregnancy within the data set (the first was retained), or chronic maternal conditions that may lead to indicated delivery, including diabetes mellitus, chronic hypertension, cardiovascular disease, placental previa, or human immunodeficiency virus–positive status. Finally, we removed the 2 centers with more than 5% missing data for hypertensive outcomes (n = 114,651). All women who developed a hypertensive complication of pregnancy were included in the final cohort of low-risk pregnancies in the expectant management group.

As previously described, we then identified women with elective induction of labors.6 and 21 A predefined variable indicated whether a women had an induction of labor and did not include those receiving only labor augmentation or with less than 2 vaginal examinations. Inductions categorized as elective had no other indications for induction provided with no obstetric, fetal, or maternal conditions complicating the pregnancy.

Study outcomes

Subjects were divided by week of gestational age at delivery (Figure). Given the limitations of pregnancy dating and the size of our data set, we chose to evaluate gestational age by week rather than day. Those with an induction of labor coded as elective were the cases of eIOL at each week of gestation. Those not electively induced and who delivered after that week of gestation were considered to be expectantly managed in that week of gestation.

The primary outcome was the frequency of developing a hypertensive complication of pregnancy. The database included codes for gestational hypertension, preeclampsia, and eclampsia. These were combined for a composite outcome of pregnancy-induced hypertensive disorders (PIH). The definitions were based on the contemporaneous ACOG guidelines (published in 2002),22 and the diagnosis was made based on the clinical judgment of the delivering provider. We assumed the diagnosis of a hypertensive disorder was made within the same week as the gestational age of delivery and that for women who developed hypertensive complications, they did not have that complication prior to the week of their delivery.

Secondary outcomes included mode of delivery and composites for maternal and neonatal comorbidities. Mode of delivery was categorized as a nonoperative vaginal delivery, an operative vaginal delivery (requiring vacuum or forceps assistance), or cesarean delivery. Maternal outcomes included bleeding (blood products, abruption, postpartum hemorrhage, uterine rupture, hysterectomy), maternal intensive care unit admission or death, infections (intrapartum fevers, chorioamnionitis, endomyometritis, wound separation), lacerations (third- or fourth-degree perineal, sulcal, or cervical), and shoulder dystocia.

Neonatal outcomes included a composite of major comorbidities (birth injuries, sepsis, pneumonia, intraventricular hemorrhage, aspiration, hypoxic ischemic encephalopathy, respiratory distress syndrome, seizures, oliguria, myocardial injury, ventilator use, continuous positive airway pressure use, transfusions, or surfactant use), a composite of respiratory morbidities (oxygen use, continuous positive airway pressure use, transient tachypnea of the newborn, or surfactant administration), or perinatal death (intrauterine fetal demise or neonatal demise).

Statistical analysis

The occurrence of the primary outcome was determined for those women expectantly managed in a particular week of gestation until the next week of gestation and compared with those with an eIOL in the same week (for example, those with an eIOL in at 37+0 to 37+6 weeks were compared with women expectantly managed through the 37th week and thus delivered at 38+0 weeks or later). The frequencies of maternal and neonatal outcomes were then compared between those with an eIOL and those expectantly managed who did or did not develop a hypertensive complication of pregnancy. A secondary analysis compared women electively induced each week with those who delivered within the same week (for example, the eIOL at 37+0 to 37+6 weeks were compared with women who delivered also within the same week).

Categorical variables were compared with χ2 or Fisher exact tests, whereas student t tests or an analysis of variance was used for continuous variables, as appropriate. To adjust for possible confounding factors, the primary outcome, a logistic regression was performed, controlling for maternal age, race/ethnicity, parity, body mass index (BMI) at delivery, insurance status, and type of hospital. Centers with more than 5% missing data for an outcome were removed from the analysis on that specific outcome. We performed all analyses using statistical software (SAS, version 9.4; SAS Institute Inc, Cary, NC).

Results

Patients

Our low-risk patient population included 114,651 women. Table 1 presents the maternal demographic characteristics for the cohort, comparing those with an eIOL with those expectantly managed who did or did not develop a hypertensive disorder of pregnancy. Overall, the cohort tended to be nulliparous (49.0%), white (51.4%), and overweight or obese (84.5%), with the majority having private insurance (58.9%) and delivering at a teaching hospital (90.1%). Women who developed a hypertensive complication were significantly younger, more obese, and more likely to be nulliparous when compared with either women with an eIOL or those expectantly managed who did not develop a hypertensive complication.

Table 1 Demographic characteristics

Variable Referent (n = 12,772) no PIH (n = 96,688) PIH (n = 5191)
n SD or % n SD or % n SD or %
Maternal age, y 27.7 5.2 27.0 6.1 26.8 6.2
Nulliparous 3986 31.2 48,746 50.4 3443 66.3
BMI at delivery, kg/m2 30.0 5.4 30.1 5.6 33.5 6.7
Private insurance 9083 71.1 54,919 56.8 3536 68.1
Teaching hospital 9373 73.4 89,214 92.3 4656 89.7
Race/ethnicity
 African American 1106 8.7 19,864 20.5 945 18.2
 White 9744 76.3 46,194 47.8 2999 57.8
 Hispanic 1079 8.5 18,378 19.0 732 14.1
 Asian 303 2.8 4506 4.7 194 3.7
 Other 540 4.2 7746 8.0 321 6.2
Gestational age at delivery, wks 39.4 0.7 39.3 1.1 38.9 1.1
 37 217 1.7 9645 10.0 978 18.8
 38 1296 10.2 21,121 21.8 1446 27.9
 39 7437 58.2 30,720 31.8 1498 28.9
 40 3822 29.9 25,021 25.9 1011 19.5
 41 10,181 10.5 258 5.0

The referent group includes all women with an eIOL.

BMI, body mass index; PHI, pregnancy-induced hypertensive disorders.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

Study outcomes

The occurrence of hypertensive disorders for those expectantly managed by week of gestation is presented in Table 2 and Table 3. Overall, 5191 women expectantly managed (5.1% of the entire expectantly managed cohort) developed a hypertensive disorder of pregnancy. By week, the frequency of developing any pregnancy-related hypertension in women expectantly managed until at least the next week of gestation (Table 2) was 4.1% at 37 weeks, 3.5% at 38 weeks, 3.2% at 39 weeks, and 2.5% at 40 weeks.

Table 2 Total hypertensive complications by week in those expectantly managed after the week of eIOL in all remaining patients

Week Referent Expectantly managed P value
n % n %
37 0/217 0 4213/103,811 4.1 < .001
38 0/1296 0 2767/79,948 3.5 < .001
39 0/7437 0 1269/40,293 3.2 < .001
40 0/3822 0 258/10,439 2.5 < .001

eIOL, elective induction of labor.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

Table 3 Total hypertensive complications by week in those expectantly managed within the same week as eIOL

Week Referent Expectantly managed P value
n % n %
37 0/217 0 978/10,623 9.2 < .001
38 0/1296 0 1446/22,567 6.4 < .001
39 0/7437 0 1498/32,218 4.7 < .001
40 0/3822 0 1011/26,032 3.9 < .001

The referent group includes all women with an eIOL.

eIOL, elective induction of labor.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

When evaluating the cases expectantly managed but who ultimately delivered within the same week (Table 3), the frequency of hypertensive complications were as follows: 9.2% in the 37th week, 6.4% in the 38th week, 4.7% in the 39th week, and 3.9% in the 40th week. Table 4 presents the specific type of pregnancy-related hypertensive disorder diagnosed for those expectantly managed. Preeclampsia was the most common diagnosis, whereas eclampsia was the most infrequent. This was true for subjects expectantly managed until the next week of gestation and for those expectantly managed but delivering within the same week of gestation.

Table 4 Each type of hypertensive complication by week in those expectantly managed after the week of eIOL in all remaining patients

Week of gestation 37 38 39 40
n 103,811 79,948 40,293 10,439
Gestational HTN 1414 1.36% 891 1.11% 385 0.96% 60 0.57%
Preeclampsia 2773 2.67% 1856 2.32% 873 2.17% 196 1.88%
Eclampsia 26 0.03% 20 0.03% 11 0.03% 2 0.02%
All PIH 4213 4.06% 2767 3.46% 1269 3.15% 258 2.47%

eIOL, elective induction of labor; HTN, hypertension; PHI, pregnancy-induced hypertensive disorders.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

We next evaluated whether the development of a hypertensive disorder of pregnancy affected the mode of delivery (Table 5 and Table 6). For those expectantly managed until the next week of gestation who developed a hypertensive complication, cesarean delivery occurred more often when compared with either the eIOL group or those who were expectantly managed but without development of a hypertensive disorder of pregnancy. eIOL consistently was associated with the lowest observed frequency of cesarean delivery at each week of gestation when compared with either the expectant management group (P < .001 for each week).

Table 5 Each type of hypertensive complication by week in those expectantly managed within the same week as eIOL

Week of gestation 37 38 39 40 Total
n 10,623 22,567 32,218 26,032 91,440
Gestational HTN 315 2.97% 523 2.32% 506 1.57% 325 1.25% 1669 1.71%
Preeclampsia 650 6.12% 917 4.06% 983 3.05% 677 2.60% 3227 3.31%
Eclampsia 13 0.12% 6 0.03% 9 0.03% 9 0.03% 37 0.04%
All PIH 978 9.21% 1446 6.41% 1498 4.65% 1011 3.88% 4933 5.06%

eIOL, elective induction of labor; HTN, hypertension; PHI, pregnancy-induced hypertensive disorders.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

Table 6 Mode of delivery by week in those with an eIOL, expectantly managed without PIH, or developing PIH after the week of eIOL

Week Nonoperative vaginal delivery Reference, SVD for eIOL, eIOL, no PIH
Referent No PIH PIH P value eIOL vs no PIH P value eIOL vs PIH P value no PIH vs PIH aOR (95% CI), eIOL vs no PIH aOR (95% CI), eIOL vs PIH aOR (95% CI), no PIH vs PIH
n % n % n %
37 197/217 90.8 80,086/99,598 80.4 2804/4213 66.6 < .001a < .001a < .001a 2.38 (1.45–3.92)a 3.37 (2.01–5.66)a 1.34 (1.24–1.45)a
38 1132/1296 87.4 61,131/77,181 79.2 1777/2767 64.2 < .001a < .001a < .001a 1.73 (1.45–2.07)a 2.45 (1.94–3.10)a 1.43 (1.30–1.58)a
39 6597/7437 88.7 29,323/39,024 75.1 749/1269 59.0 < .001a < .001a < .001a 1.43 (1.31–1.55)a 2.30 (1.93–2.74)a 1.50 (1.30–1.74)a
40 2956/3822 77.3 7185/10,181 70.6 145/258 56.2 < .001a < .001a < .001a 1.31 (1.18–1.46)a 2.27 (1.60–3.22)a 1.73 (1.23–2.43)a
Week Operative vaginal delivery Reference, OVD for eIOL, eIOL, no PIH
Referent No PIH PIH P value, eIOL vs no PIH P value, eIOL vs PIH P value, no PIH vs PIH aOR (95% CI), eIOL vs no PIH aOR (95% CI), eIOL vs PIH aOR (95% CI), no PIH vs PIH
n % n % n %
37 9/217 4.2 6926/99,598 7.0 402/4213 9.5 .10 .008a < .001a 0.81 (0.41–1.59) 0.62 (0.31–1.25) 0.81 (0.72–0.91)a
38 53/1296 4.1 5588/77,181 7.2 261/2767 9.4 < .001a < .001a < .001a 0.70 (0.53–0.93)a 0.56 (0.39–0.80)a 0.83 (0.71–0.96)a
39 526/7437 7.1 2971/39,024 7.6 126/,269 9.9 .11 < .001a .002a 1.06 (0.95–1.18) 0.94 (0.72–1.21) 0.79 (0.64–0.98)a
40 373/3822 9.8 743/10,181 7.3 18/258 7.0 < .001a .14 .84 1.15 (0.99–1.33) 1.32 (0.73–2.40) 1.07 (0.60–1.93)
Week Cesarean delivery Reference, CS for eIOL, eIOL, no PIH
Referent No PIH PIH P value, eIOL vs no PIH P value, eIOL vs PIH P value, no PIH vs PIH aOR (95% CI) eIOL vs no PIH aOR (95% CI) eIOL vs PIH aOR (95% CI) no PIH vs PIH
n % n % n %
37 11/217 5.1 12,586/99,598 12.6 1007/4213 23.9 < .001a < .001a < .001a 0.31 (0.16–0.60)a 0.23 (0.12–0.46)a 0.76 (0.69–0.83)a
38 111/1296 8.6 10,462/77,181 13.6 729/2767 26.4 < .001a < .001a < .001a 0.56 (0.45–0.94)a 0.40 (0.30–0.52)a 0.70 (0.62–0.78)a
39 314/7437 4.2 6730/39,024 17.3 394/1269 31.1 < .001a < .001a < .001a 0.44 (0.39–0.50)a 0.32 (0.26–0.40)a 0.68 (0.58–0.80)a
40 493/3822 12.9 2253/10,181 22.1 95/258 36.8 < .001a < .001a < .001a 0.61 (0.54–0.70)a 0.31 (0.21–0.45)a 0.52 (0.36–0.74)a

a Values are statistically significant.

The referent group includes all women with an eIOL.

aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; PHI, pregnancy-induced hypertensive disorders; OVD, operative vaginal delivery; SVD, spontaneous vaginal delivery.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

Additionally, the frequency of operative vaginal delivery was also higher for those women expectantly managed who developed PIH at 37, 38, and 39 weeks. Interestingly, eIOL was associated with a decreased risk of operative delivery at 37, 38, and 39 weeks of gestation when compared with the expectantly managed subjects who did not develop a pregnancy-associated hypertensive complication.

In a logistic regression adjusted for confounding variables (maternal age, race/ethnicity, parity, BMI at delivery, insurance status, and type of hospital), the risk of cesarean delivery remained significantly lower at each week of gestation for women with a eIOL when compared with either women who were expectantly managed who developed PIH or when compared with those expectantly managed without the development of PIH. Women who were expectantly managed but without the development of PIH also had a lower adjusted odds of cesarean delivery at each week of gestation when compared with those expectantly managed but who developed PIH. These trends were similar for women expectantly managed but delivering within the same week of pregnancy (Supplemental Table).

Table 7 presents the secondary outcome of maternal and neonatal composite morbidities. For only those women who were expectantly managed, the development of PIH was associated with a significantly increased frequency of maternal intensive care unit (ICU) admissions or death at 37 (0.3% vs 0.8%, P < .001), 38 (0.3% vs 0.8%, P < .001), and 39 weeks (0.3% vs 1.2%, P < .001) and maternal infections at all weeks (8.8% vs 12.5%, P < .001 at 37 weeks; 9.3% vs 13.9%, P < .001 at 38 weeks; 11.3% vs 16.5%, P < .001 at 39 weeks; 13.3% vs 23.1%, P < .001 at 40 weeks).

Table 7 Maternal morbidities by week in those with a eIOL, expectantly managed without PIH, or developing PIH after the week of eIOL

Week Maternal bleeding complications
Referent No PIH PIH P Value, referent vs no PIH P Value, referent vs PIH P Value, no PIH vs PIH
n % n % n %
37 10/197 5.1 5649/78,657 7.2 316/3694 8.6 .140 .040a .002a
38 63/1190 5.3 4331/60,562 7.2 189/2426 7.8 .002a < .001a .230
39 716/6969 10.3 1927/29,591 6.5 83/1094 7.6 < .001a .030a .160
40 248/3140 7.9 445/7570 5.9 17/222 7.7 .180 .500a .270
Week Maternal intensive care admission or death
Referent no PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 1/214 0.5 204/79,702 0.3 22/2945 0.8 .43 1.00 < .001a
38 1/1283 0.1 154/61,222 0.3 15/1792 0.8 .39 .003a < .001a
39 9/7411 0.1 81/29,601 0.3 9/737 1.2 .02a < .001a < .001a
40 5/3706 0.1 23/7336 0.3 1/119 0.8 .07 .170 .320
Week Maternal infections
Referent No PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 5/209 2.4 7644/86,931 8.8 488/3920 12.5 < .001a < .001a < .001a
38 28/1265 2.2 6267/67,260 9.3 357/2566 13.9 < .001a < .001a < .001a
39 144/7404 1.9 3750/33,258 11.3 192/1165 16.5 < .001a < .001a < .001a
40 184/3679 5.0 1113/8398 13.3 53/229 23.1 < .001a < .001a < .001a
Week Third- or fourth-degree perineal or sulcal lacerations
Referent No PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 9/217 4.2 6440/99,598 6.5 332/4213 7.9 .170 .040a < .001a
38 56/1296 4.3 5187/77,181 6.7 225/2767 8.1 < .001a < .001a .004a
39 285/7437 3.8 2899/39,024 7.4 103/1269 8.1 < .001a < .001a .360
40 265/3822 6.9 767/10,181 7.5 12/258 4.7 .230 .160 .080
Week Shoulder dystocia
Referent No PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 0/217 0 1540/99,598 1.6 53/4213 1.3 .090 .11 .14
38 9/1296 0.7 1267/77,181 1.6 33/2767 1.2 .008a .14 .07
39 133/7437 1.8 667/39,024 1.7 11/1269 0.9 .630 .02a .02a
40 73/3822 1.9 170/10,181 1.7 1/258 0.4 .330 .09 .13
Week Neonatal complication composite
Referent No PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 9/217 4.1 2755/99,598 2.8 139/4213 3.3 .230 .500 .04a
38 26/1296 2 2185/77,181 2.8 94/2767 3.4 .080 .010a .08
39 109/7437 1.5 1258/39,024 3.2 41/1269 3.2 < .001a < .001a .99
40 99/3723 2.6 359/10,181 3.5 9/258 3.5 .006a .380 .97
Week Neonatal respiratory complications
Referent no PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 9/217 4.2 2286/99,598 2.3 122/4213 2.9 .070 .290 .01a
38 21/1296 1.6 1820/77,181 2.4 77/2767 2.8 .080 .020a .15
39 90/7437 1.2 1013/39,024 2.6 34/1269 2.7 < .001a < .001a .85
40 73/3822 1.9 299/10,181 2.9 8/258 3.1 .020a .190 .88
Week Perinatal death
Referent No PIH PIH P value, referent vs no PIH P value, referent vs PIH P value, no PIH vs PIH
n % n % n %
37 0/217 0 334/99,598 0.3 16/4213 0.4 1.00 1.00 .62
38 0/1296 0 235/77,181 0.3 11/2767 0.4 .004a .02a .39
39 13/7437 0.2 119/39,024 0.2 5/1269 0.4 .050a .16 .59
40 8/3822 0.2 30/10,181 0.3 0/258 0.0 .230 .16 .47

a Values are statistically significant.

The referent group includes all women with an eIOL.

eIOL, elective induction of labor; PHI, pregnancy-induced hypertensive disorders.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

Maternal bleeding complications, severe obstetrical lacerations, and shoulder dystocia was overall similar between those who were expectantly managed who did or did not develop a hypertensive complication of pregnancy. When compared with the eIOL group, the expectantly managed women with and without a hypertensive complication had in general significantly higher rates of maternal bleeding complications, maternal ICU admission or death, maternal infections, and severe obstetrical lacerations. There were no differences in the rates of shoulder dystocia. Comparisons for those expectantly managed but delivering within the same week were similar.

Composite neonatal morbidities were highest at each week of gestation for those subjects expectantly managed who developed a hypertensive complication when compared with either those expectantly managed who did not develop a hypertensive complication or when compared with those with an eIOL. By 38 weeks, eIOL had the lowest observed frequency of either composite neonatal morbidities or isolated respiratory morbidities.

Stillbirth was noted to be a complication of expectant management of any pregnancy. At 37 weeks, 230 stillbirths occurred in those expectantly managed until the next week of pregnancy (9 occurring for those who developed PIH) with 104 observed neonatal deaths (7 occurring for those who developed PIH) in the same cohort. For those expectantly managed at 38 weeks, 144 stillbirths were observed with 91 neonatal deaths. At 39 weeks, 72 stillbirths were observed in those expectantly managed until at least 40 weeks with 47 neonatal deaths. No neonatal deaths were observed in those with a eIOL at either 37 or 38 weeks with a total of 13 neonatal deaths reported for those with an elective induction of labor at 39 weeks.

Comment

Using a cohort of low-risk pregnancies within the Consortium on Safe Labor database, we examined the incidence of hypertensive disorders of pregnancy for women who were expectantly managed at term by week of gestation. For our primary outcome, we observed that there is a maternal risk of developing a hypertensive complication (2.5–9.2%) when a pregnancy is expectantly managed at term.

Additionally, for those women who are expectantly managed and develop a hypertensive disorder, there are significant associated maternal and neonatal consequences including the following: increased cesarean delivery, operative vaginal delivery, maternal infection, admission to the ICU/death, and composite neonatal morbidities including respiratory morbidities. In general, the lowest observed frequencies of cesarean delivery and maternal/neonatal complications were for those with a eIOL, regardless of week of gestation, when compared with women expectantly managed with or without a subsequent hypertensive complication.

As several recent publications3, 4, 5, 6, 7, 8, 9, and 23 have discussed, expectant management of a term pregnancy is not without consequence to both the mother and fetus. Risks that have previously been highlighted for expectant management at term include increased risks of cesarean delivery, maternal infection, stillbirth, and composite neonatal morbidities. These data are in contrast to papers that have evaluated only the frequency of neonatal morbidities by week of delivery and concluded that expectant management at term is desirable for neonatal benefit.1, 2, 24, 25, and 26 Such analyses have not accounted for all fetal risks of expectant management and omit the risk of nondelivery for the mother.

The data reported herein moves this area of study forward by describing the risk of a common maternal complication of pregnancy during expectant management of a low-risk term pregnancy by week of gestation. Prior publications have reported on the general incidence of hypertensive complications for all pregnancies.10, 14, 15, 16, 17, and 18 To our knowledge, the estimation of the risk of developing a hypertensive complication of pregnancy during expectant management at term has not previously been reported.

Additionally, the current recommendations regarding the optimal time of term delivery has not included a discussion of the potential consequences of avoiding an elective early term birth. These data demonstrate that expectant management at term is not risk free. Even the development of one complication during expectant management, in this case a hypertensive complication, confers additional risk with adverse maternal and neonatal consequences.

Our data have several limitations. First, although we attempted to compare elective induction of labor vs expectantly managed women, this was not a randomized trial. This study is using a cross-sectional data set to address a longitudinal question. We attempted to control for confounding in our multivariate analysis, yet potential selection bias by indication may be possible, including differences in cervical examination prior to the start of labor. For example, our cohort was 84.5% overweight or obese, higher than the current reported national prevalence. This selection bias may have induced an overestimation of maternal and neonatal morbidity and mortality associated with expectant management because many of our outcomes have also been related to maternal BMI. However, as an intended representation of the entire US obstetric population, the Consortium on Safe Labor represents the best available data set to evaluate the outcomes included in this analysis.

We had a small sample size of only 217 eIOL patients at 37 weeks’ gestation, limiting the statistical power at this gestational age, particularly for the rarer outcomes such as neonatal morbidities. We are not able to know exactly when a hypertensive complication was diagnosed, so a woman who started an eIOL and later developed a hypertensive complication was included in the expectant management group to avoid including medically indicated inductions for PIH from being included in the eIOL group.

Lastly, despite national guidelines, each site may have used slightly different diagnostic criteria. Nonetheless, because this analysis is based on medical records data (and not administrative data), it is the best data possible short of having an observer at each delivery or a large randomized trial.

In conclusion, these data suggest that expectant management at term is not a risk-free proposition. Recommendations about the optimal time of delivery that singularly focus on neonatal morbidities calculated by week of delivery will continue to overestimate the benefit of expectant management and underestimate the risks, particularly for the mother. This is especially true when data are not properly analyzed by the true obstetric choices of elective delivery vs expectant management, in which the risks of delivery and nondelivery can be better quantified. As these data show, outcomes for mom and baby are complex and optimal benefits for the fetus may be in direct conflict with benefits for the mother. Moreover, the development of an adverse consequence for the mother may directly result in adverse outcomes for the fetus.

The only way to correctly assess the optimal time of delivery is the performance of randomized controlled trials in which women are randomly allocated to eIOL at 37 or 38 or 39 or 40 weeks of gestation vs expectant management until 41 weeks of gestation and to evaluate both maternal and perinatal outcomes. Until such data are available, appropriate counseling of term gravid patients must include our best estimates of the risks of delivery and nondelivery.

Acknowledgments

We thank S. Katherine Grantz, MD, MS (Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD) and Jun Zhang, PhD (MOE and Shanghai Key Laboratory of Children’s Environmental Health, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China) for their assistance in the initial study design. Institutions involved in the Consortium include the following, in alphabetical order: Baystate Medical Center, Springfield, MA; Cedars-Sinai Medical Center Burnes Allen Research Center, Los Angeles, CA; Christiana Care Health System, Newark, DE; Georgetown University Hospital, MedStar Health, Washington, DC; Indiana University Clarian Health, Indianapolis, IN; Intermountain Healthcare and the University of Utah, Salt Lake City, UT; Maimonides Medical Center, Brooklyn, NY; MetroHealth Medical Center, Cleveland, OH; Summa Health System, Akron City Hospital, Akron, OH; The EMMES Corpo, Rockville MD (data coordinating center); University of Illinois at Chicago, Chicago, IL; University of Miami, Miami, FL; and University of Texas Health Science Center at Houston, Houston, TX.

Appendix

Supplemental Table Mode of Delivery by week in those with a eIOL, expectantly managed without PIH, or developing PIH within the same week as eIOL

week Non-Operative Vaginal Delivery reference, SVD for eIOL, eIOL, no PIH
Referent no PIH PIH P eIOL v no PIH P eIOL v PIH P no PIH v PIH aOR (95CI) eIOL v no PIH aOR (95CI) eIOL v PIH aOR (95CI) no PIH v PIH
number % number % number %
37 197/217 90.8 8,284/9,645 85.9 699/978 71.5 0.04a <0.001a <0.001a 1.81 (1.10 - 2.98)a 2.32 (1.34 - 4.00)a 1.29 (1.07 - 1.55)a
38 1,132/1,296 87.4 17,823/21,121 84.4 1,027/1,446 71.0 0.004a <0.001a <0.001a 1.44 (1.20 - 1.74)a 1.75 (1.36 - 2.27)a 1.33 (1.15 - 1.54)a
39 6,597/7,437 88.7 25,211/30,720 82.1 1,028/1,498 68.6 <0.001a <0.001a <0.001a 1.13 (1.03 - 1.23)a 1.67 (1.41 - 1.97)a 1.42 (1.24 - 1.63)a
40 2,956/3,822 77.3 19,182/25,021 76.7 604/1,011 59.7 0.36 <0.001a <0.001a 1.10 (1.00 - 1.21) 1.66 (1.38 - 2.00)a 1.47 (1.25 - 1.73)a
week Operative Vaginal Delivery reference, OVD for eIOL, eIOL, no PIH
Referent no PIH PIH P eIOL v no PIH P eIOL v PIH P no PIH v PIH aOR (95CI) eIOL v no PIH aOR (95CI) eIOL v PIH aOR (95CI) no PIH v PIH
number % number % number %
37 9/217 4.2 531/9,645 5.5 81/978 8.3 0.38 0.04a <0.001a 0.91 (0.46 - 1.81) 0.57 (0.28 - 1.29) 0.78 (0.59 - 1.03)
38 53/1,296 4.1 1,285/21,121 6.1 141/1,446 9.8 0.003a <0.001a <0.001a 0.79 (0.59 - 1.06) 0.60 (0.40 - 0.88)a 0.75 (0.61 - 0.92)a
39 526/7,437 7.1 2,091/30,720 6.8 135/1,498 9.0 0.42 0.009a 0.001a 1.22 (1.09 - 1.36)a 1.04 (0.82 - 1.32) 0.82 (0.66 - 1.00)
40 373/3,822 9.8 1,855/25,021 7.4 108/1,011 10.7 <0.001a 0.38 <0.001a 1.16 (1.02 - 1.32)a 0.86 (0.66 - 1.12) 0.74 (0.58 - 0.93)a
week Cesarean Delivery reference, CS for eIOL, eIOL, no PIH
Referent no PIH PIH P eIOL v no PIH P eIOL v PIH P no PIH v PIH aOR (95CI) eIOL v no PIH aOR (95CI) eIOL v PIH aOR (95CI) no PIH v PIH
number % number % number %
37 11/217 5.1 830/9,645 8.6 198/978 20.3 0.07a <0.001a <0.001a 0.43 (0.22 - 0.83)a 0.37 (0.18 - 0.77)a 0.79 (0.64 - 0.99)a
38 111/1,296 8.6 2,013/21,121 9.5 278/1,446 19.2 0.25 <0.001a <0.001a 0.68 (0.54 - 0.85)a 0.60 (0.44 - 0.81)a 0.79 (0.67 - 0.94)a
39 314/7,437 4.2 3,418/30,720 11.1 335/1,498 22.4 <0.001a <0.001a <0.001a 0.60 (0.52 - 0.68)a 0.44 (0.35 - 0.54)a 0.69 (0.59 - 0.81)a
40 493/3,822 12.9 3,984/25,021 15.9 299/1,011 29.6 <0.001a <0.001a <0.001a 0.77 (0.69 - 0.87)a 0.56 (0.45 - 0.69)a 0.73 (0.61 - 0.88)a

a Values are statistically significant.

Gibson et al. Weekly incidence of hypertensive disorders in low-risk term pregnancies. Am J Obstet Gynecol 2016.

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Footnotes

a Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, MetroHealth Medical Center–Case Western Reserve University, Cleveland, OH

b Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Loyola University Medical Center, Maywood, IL

Corresponding author: Kelly S. Gibson, MD.

The views expressed herein are those of the authors, which do not necessarily represent the decisions or the stated policy of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health.

The authors report no conflict of interest.

The Consortium on Safe Labor was funded by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, through Contract No. HHSN267200603425C.

Cite this article as: Gibson KS, Waters TP, Bailit JL. A risk of waiting: the weekly incidence of hypertensive disorders and associated maternal and neonatal morbidity in low-risk term pregnancies. Am J Obstet Gynecol 2016;214:389.e1-12.