Pre-pregnancy blood pressure and body mass index trajectories and incident hypertensive disorders of pregnancy

Abstract

There are few studies examining patterns in body mass index (BMI) and blood pressure (BP) and subsequent hypertensive disorders of pregnancy (HDPs). We examined the association of BMI (n = 1342) or BP (n = 2266) trajectories in the 5 years preceding birth with HDPs using adjusted logistic regression. Compared to normal-weight BMI and low-normal BP groups, membership to the overweight BMI group (OR: 2.95, 95%CI: 1.57–5.53, p = 0.001) and higher-normal (OR: 2.74, 95%CI:1.49–5.04, p = 0.001) and prehypertensive (OR:7.27, 95%CI: 3.29–16.06, p < 0.001) BP groups were associated with higher odds of HDPs. Our data suggest maintaining normal-weight and low-normal BP in the years preceding pregnancy may help avoid HDPs.

1. Introduction

Hypertensive disorders of pregnancy (HDPs), including de novo hypertension in pregnancy, preeclampsia, and eclampsia, occur in 5–10% of all pregnancies in the United States and are a leading cause of maternal and fetal death [1]. HDPs are also associated with longer-term maternal cardiovascular disease risk [2,3]. A history of HDP is a sex-specific risk factor for cardiovascular disease [4]. The mechanisms by which HDPs contribute to longer-term cardiovascular disease are not fully understood, but HDPs and cardiovascular disease share common risk factors, including obesity and hypertension [4].

Obesity and hypertension measured at a single time point immediately preceding or during early pregnancy are associated with greater likelihood of developing an HDP [5–7]. The value of describing trajectories of cardiovascular disease risk factors (rather than single time point measurements) in relation to subclinical cardiovascular disease has recently been reported [8]. It is unknown whether risk factor trajectories in the years preceding pregnancy predict which women will go on to develop HDPs.

Our purpose was to determine the association between body mass index (BMI) and blood pressure (BP) trajectories in the 5 years preceding pregnancy and incident HDPs. To increase our sample size and ensure a race/ethnically diverse cohort, we abstracted BMI and BP measurements from medical records of patients who had a singleton birth at a large, urban teaching hospital. We used this data to test our hypothesis that sustained higher or increasing BMI and BP in the 5 years prior to pregnancy would be associated with higher odds of having an HDP in the index pregnancy.

2. Methods

2.1. Participants

This was a retrospective cohort study of women who delivered at Northwestern Medicine Hospitals in 2010. Women were included if: i) they gave birth at 20–42 weeks gestation following a singleton pregnancy, ii) were over 18 years old at the time of delivery, and iii) had at least one annual BMI or BP measurement recorded in their medical charts (obtained during in-patient or out-patient visits) in three of the five years preceding the index birth. Our total n = 1342 women for the BMI analyses, and n = 2266 women for the BP analyses. Eighteen of the 2266 women included in our analyses (0.8%) had gestational age < 24 weeks; 1326 women were included in both analyses (Tables 1A and 1B).

Table 1A.

Participant characteristics by BMI trajectory group.

	Normal Weight N = 973	Overweight N = 311	Obese N = 58
Age at delivery (yr)	34 (4)	34 (4)	34 (4)
SBP (mmHg)	110 (10)	114 (10)	121 (9)
BMI (kg/m2)	21.6 (2.0)	27.4 (2.8)	39.4 (5.9)
Race (%)
White	77	65	38
Black	3	11	34
Hispanic	4	3	3
Asian/Pacific Islander	<1	<1	2
Native American	<1	<1	0
Unknown	14	20	22
Chronic conditions
Hypertension	2	3	22
Diabetes	1	2	9
Heart disease	3	2	5
Odds Ratio for HDP (95%CI)	reference	2.95 (1.57–5.53)	3.03 (0.91–10.07)

SBP: systolic blood pressure; BMI: body mass index; HDP: hypertensive disorder of pregnancy.

Table IB.

Participant characteristics by BP trajectory group.

	Low-Normal N = 1061	Higher-Normal N = 1049	Prehypertensive N = 156
Age at delivery (yrs)	34 (4)	34 (4)	34 (4)
SBP (mmHg)	105 (7)	115 (8)	129 (12)
BMI (kg/m2)	22.2 (3.2)	24.6 (4.6)	29.8 (8.6)
Race (%)
White	76	75	64
Black	3	7	12
Hispanic	6	2	3
Asian/Pacific Islander	1	<1	<1
Native American	<1	<1	0
Unknown	14	14	20
Chronic conditions (%)
Hypertension	<1	1	22
Diabetes	<1	2	1
Heart disease	3	2	3
Odds Ratio for HDP (95%CI)	reference	2.74 (1.49–5.04)	7.27 (3.29–16.06)

SBP: systolic blood pressure; BMI: body mass index; HDP: hypertensive disorder of pregnancy.

2.2. Study measurements

All data were abstracted from the patient’s medical record using the Northwestern Medicine Enterprise Data Warehouse [9]. If a patient had more than one measurement in a single year, the median value was used for analysis. HDP was identified as an affirmative response for “preeclampsia”, “gestational hypertension”, or “hypertension in pregnancy” in the medical chart at the time of admission for childbirth. Demographic information and medical history were obtained from forms completed upon admission for delivery.

2.3. Analyses

We constructed trajectory groups of women with similar underlying patterns in pre-pregnancy BMI and systolic BP using latent class trajectory analysis [10]. We tested for normality with Shapiro-Wilk tests and between-group differences in descriptive characteristics using ANOVA and chi² tests in the subset of women with a data point at 5 years prior to pregnancy. Data for descriptive characteristics are mean ± SD. We tested whether assignment to the higher BMI or BP trajectory groups (versus lowest trajectory group) was associated with higher odds of HDP in separate analyses using logistic regression adjusted for maternal age at delivery, race, and maternal history of hypertension, diabetes, and heart problems. We conducted a sensitivity analysis by adding systolic BP at year 4–5 prior to delivery as a covariate in our model. Stata version 14.0 was used for analyses.

3. Results & discussion

3.1. Trajectory groups

We identified three distinct trajectory groups for BMI: normal weight (n = 973, mean BMI at 5 yrs prior to delivery = 21.6 ± 2 kg/m²), overweight (n = 311, mean BMI = 27.4 ± 2 kg/m²), and obese (n = 58, mean BMI = 39.4 ± 6 kg/m²), Fig. 1A, Participants in the highest BMI group had higher systolic BP and were more likely to have a history of hypertension, p < 0.001 for all. We identified three BP trajectory groups: low-normal (n = 1061, mean systolic BP at 5 yr prior to delivery = 105 ± 7 mmHg), higher-normal (n = 1069, mean systolic BP = 115 ± 8 mmHg), and prehypertensive (n = 156, mean systolic BP = 129 ± 12 mmHg), Fig. 1B, Participants in the prehypertensive BP group had a higher BMI and were more likely to have a history of hypertension, p < 0.001. Race composition of the groups varied (p < 0.001); proportion of black women increased with increasing BMI and BP trajectory groups. Mean age at delivery was 34 ± 4 years for all groups.

Fig. 1A.

BMI trajectories in the 5 years preceding index pregnancy.

Fig. 1B.

Systolic BP trajectories in the 5 years preceding index pregnancy.

3.2. Regression

Using the normal weight BMI and low-normal BP trajectory groups as references, assignment to the overweight BMI trajectory (adjusted odds ratio [aOR]: 2.95, 95% CI: 1.57–5.53, p = 0.001), higher-normal BP trajectory (aOR: 2.74, 95% CI: 1.49–5.04, p = 0.001), and prehypertensive trajectory groups (aOR: 7.27, 95% CI: 3.29–16.06, p < 0.001) were significantly associated with HDP. Interestingly, assignment to the high-normal BP trajectory group was associated with greater odds of HDP, even though the mean systolic BP in this group was only 115 mmHg. These data suggest that achieving and maintaining pre-pregnancy systolic BP under the national recommendation of 120 mmHg may be useful for avoiding HDPs.

Assignment to the obese BMI trajectory was nearly significantly associated with HDP (OR: 3.03, 95% CI: 0.91–10.07, p = 0.07). We believe the association between assignment to the obesity trajectory group and HDPs did not reach statistical significance because of the small sample size in this subgroup. The OR of 3.03 suggests elevated risk of HDPs in obese women. Regression results were qualitatively unchanged after we included BMI or BP at 4–5 years pre-pregnancy in our regression models.

Our study demonstrated that BMI and BP patterns in the years prior to pregnancy are associated with HDPs. Our findings extend prior work showing that obesity and elevated BP immediately preceding pregnancy are associated with likelihood of HDPs [6,7] and suggest that the subclinical milieu that predisposes women with higher BMI and BP to HDPs may begin well before the onset of pregnancy. The results are in line with other studies that have shown that long term patterns in cardiovascular risk factors are independently linked to subclinical and overt disease [8]. Our data suggest maintaining normal-weight BMI and low-normal systolic BP in the years before pregnancy may help combat HDPs.