The role of gestational weight gain in hypertensive disorders of pregnancy: open prospective cohort study

Objective

To determine the impact of Gestational Weight gain and Prepregnancy weight as risk factors for Pregnancy Induced Hypertension.

Methods

The study was a prospective open cohort study at antenatal clinic of Lagos University Teaching Hospital, Nigeria.  Ninety pregnant women who were previously not hypertensive prior to conception and booking were recruited for the study. The blood pressure and weight were done at booking and they were followed up till delivery. The pregnant women had no chronic medical condition. The  P value of < 0.05 was considered significant.

Results

The frequency of pregnancy induced hypertension was 43 (47.8%). The overall gestational weight gain and prepregnancy weight in pregnant women who developed pregnancy induced hypertension were compared to those without pregnancy induced hypertension. The mean overall weight gain in pregnancy was 11.75 ±4.53kg  while mean prepregnancy weight was 65.78±11.52kg. About 37 (41.1%) of the pregnant women had gestational weight gain in the obese and overweight category using the Institute of Medicine classification. The pregnant women who were in the obese and overweight category using the Institute of Medicine   classification system were 60.5%. These women had pregnancy induced hypertension while using gestational weight gain greater than 12kg, about 69.8% of woman had pregnancy induced hypertension. Meanwhile 67.4% of pregnant women with prepregnancy, Body Mass Index in the obese and overweight category had pregnancy induced hypertension (Risk ratio (95% confidence interval) 3.66 (1.53-8.75).

Conclusion

Gestational weight gain can be used as a screening tool to predict those at risk for pregnancy induced hypertension especially in pregnant women with prepregnant body mass index in the obese and overweight category in resource poor settings.

Keywords

Delivery, gestational weight gain , institute of medicine, prepregnancy weight, pregnancy induced Hypertension,

Introduction

Hypertensive disorders are one of the common complications in pregnancy accounting for about 10% of complication globally.[1] Hypertensive disorders in Pregnancy (HDP) includes Pregnancy Induced Hypertension (PIH), Pre-eclampsia and Chronic hypertension.[2,3] The aetiology of HDP remains unknown, however Gestational weight gain(GWG)  and Prepregnancy weight have been implicated as one of the risk factors for HDP especially PIH and Preeclampsia.[4] Preeclampsia is the occurrence of hypertension and proteinuria after 20 weeks of gestation while PIH is hypertension without proteinuria.[5] It is associated with increased maternal and fetal morbidity and mortality.[6,7] PIH remains a risk factor for development of chronic hypertension and other cardiovascular diseases.[8-11 ] 
There are physiological changes that occurs in a normal pregnancy such as plasma volume expansion, increase maternal caloric and nutrient intake, reduce physical activity as pregnancy advances with the uterine contents such as growing fetus, amniotic fluid and placenta. [4,12] These changes can cause weight difference of the pregnant woman from pregestational weight. However, excessive GWG and prepregnancy weight are independent and modifiable risk factor for the adverse complications of pregnancy such as PIH and preeclampsia.[13] The Institute of Medicine (IOM)  has guidelines for appropriateness of weight gain in pregnancy. The recommended weight gains for underweight (BMI < 18.5 kg/m2) 12.5–18kg, normal weight (BMI = 18.5–24.9 kg/m2) 11.5–16kg, overweight (BMI = 25.0–29.9 kg/m2) 7.0–11.5kg and obese women (BMI > 30.0 kg/m2) 5-9kg.[14]
This is an area that have not been well researched, only few studies have examined the association between IOM guidelines and risk of PIH in Nigeria and Africa generally. Most studies reported in the literatures were mainly on the impact of HDP on pregnancy outcomes rather than the risk factors for HDP. This study aims to determine the impact of GWG and Pre-pregnancy weight as risk factors for PIH. Hence the results of this study will be very useful to the clinicians in the management of HDP.

Methods

The study was an open prospective cohort, carried out at the Lagos University Teaching Hospital (LUTH), Lagos state, South Western Nigeria. The study population from which the participants were sampled consisted of pregnant women at first and second trimester who attended the antenatal clinics in LUTH during the period of recruitment and newborns of the index pregnancies.
The main outcome of this study is PIH. The inclusion criteria were pregnant Nigerian women without hypertension, those women at gestational age of within 13 to 24 weeks at the time of recruitment and those who accepted to participate and gave informed consent. Studies have showed that the gestational age at booking is generally late in Nigerians.[15-16] The exclusion criteria were pregnant women with multiple gestations from result of booking ultrasound scan or as stated in their case notes, those women with pre-gestational diabetes mellitus from history documented in booking notes, women who cannot recall their pre-pregnancy weight, those been managed for chronic medical conditions, women on medications that could affect glucose tolerance in pregnancy for example beta adrenergic agonists, steroids e.t.c as documented in booking notes.[7] and women who did not accept to participate in the study nor gave informed consent.
The sample size for the study objective was determined using a correlational formula and assuming a significance level of 0.05 in a two-tailed analysis, a moderate effect size (rho=3 according to Cohen)[8] and allowing for 20% attrition rate in view of the prospective nature of the study, a total of 90 mother to newborn pairs were recruited for the study. This sample size has a power of 80%.
The research null hypothesis states there is no relationship between GWG, Pre-pregnancy weight and PIH.
The participants were recruited through simple random sampling method between 1st March 2017 and 30th June 2017 from the antenatal clinics between gestational age within 13 to 24 weeks. The sampling frame consisted of all the pregnant women that attended and received care in the antenatal clinic. Eligible pregnant women, who met the inclusion criteria at each clinic day, were randomly selected using the table of random numbers and were invited to participate in the study. Women who gave consent to be part of the study were enrolled into the study until the desired sample size was attained. The study participants were categorized into underweight, normal weight, overweight and obesity at the time of recruitment. 
A structured study data form was used to collect information on participant’s sociodemographic, medical, obstetrics and reproductive characteristics. Maternal blood pressure, pulse rate and anthropometric characteristics were also obtained at the time of recruitment. Their prepregnancy weight was noted as well as weight at recruitment which were also recorded and followed up till 37 weeks gestation. The pregnant women blood pressure was measured using mercury sphygmomanometer in a sitting position after resting for 15 minutes. Diagnosis of HDP was made based on ACOG guidelines. Women diagnosed with HDP were managed according to standard treatment protocol and all the study participants were followed up till 37 weeks gestation.
The anthropometric measurements were taken using standard techniques.[1] Two measurements were taken and average value used. If the measurements differ by 1kg, a third measurement was taken. The average of the two was used, otherwise the average of three. This was to minimize intra and inter observational errors.
Ethical approval for the study was obtained from LUTH ethical committee (ethical approval number AM/DCST/HREC/APP/862). Informed consent was obtained from all the participants before the commencement of the study.
Data generated from clinical and biophysical parameters were analyzed using statistical package for social science (SPSS) version 26 along with Microsoft excel P value <0.05 was considered to be statistically significant. Descriptive statistics were presented as mean and 95% confidence interval for data that were normally distributed. The proportion of pregnant women who were obese, overweight, normal weight and underweight were determined. The mean systolic and diastolic blood pressure was determined for each group of pregnant women. The average blood pressure and weight gain per week was noted for each pregnant woman. Tables was used to present the data obtained. Chi square statistics was used to compare proportions between the groups of pregnant women based on pre-pregnancy weight and weight gain in pregnancy. Risk ratio and 95% confidence interval were used to determine clinical significance. The strength of predictive value of a variable was determined using risk ratio.

Results

Table 1 showed the baseline characteristics of the pregnant women. The overall average age was 32.61 ± 4.89 years while the average prepregnancy weight was 65.78 ± 11.52kg. 
Those women with PIH, the mean age was 32.40±5.27 years and those without PIH, the mean age was 32.81±4.56 years. The frequency of PIH was 43 (47.8%).
The women who developed PIH had a higher blood pressure at booking  and  also higher blood pressure at delivery. The mean rise in blood pressure per gestational age was statistically significant (p value 0.001).
Table 4 compared the initial prepregnancy weight, absolute weight gain in pregnancy and excessive weight gain (based on IOM classification) in the women who developed PIH and those without PIH. The average overall weight gain in pregnancy was 11.75 ±4.53kg while average prepregnancy weight was 65.78±11.52kg. Using the initial prepregnancy weight category, 67.4% of pregnant women who were categorized into the obese and overweight category had PIH (risk ratio (95% confidence interval) 3.66 (1.53-8.75). Meanwhile, 37 (41.1%) of the pregnant women using the IOM classification had excessive weight gain in the obese and overweight category. Out of these pregnant women in the obese and overweight category using IOM classification, 60.5% had PIH (risk ratio (95%confidence interval) 5.01 (2.01-12.45). While using the absolute weight gain in pregnancy greater than 12kg, 69.8% of woman had PIH.
 

Discussion

Higher prepregnancy weight has been linked to development of pregnancy induced hypertension. Women with PIH had a higher prepregnancy weight and gestational weight gain, this is similar to the findings by IOM.The IOM in 2009 similarly showed the risk of development of PIH with overweight and obese weight gain in pregnancy.[14] Several studies have shown the association and risk of hypertensive disorder in pregnancy in those with higher prepregnancy weight and excessive weight gain in pregnancy.[17-19] The risk of development of PIH increases by 5-fold with increase weight in the overweight and obese range of IOM classification (RR; 5.01) in this study. Also, this study demonstrated approximately four-fold increase risk of PIH (RR; 3.66) with prepregnancy weight in the obese and overweight women. Those with PIH also had a higher weight gain and blood pressure rise per gestational week from booking to 37 weeks of gestation. This may be linked to the relationship between overweight and obesity to insulin resistance and endothelial dysfunction.
Mori T et al [20] demonstrated that women with preeclampsia had significantly lower plasma concentrations of adiponectin but higher concentrations of leptin, plasminogen activator inhibitor-1, interleukin-6, vascular cell adhesion molecule-1, E-selectin and C-reactive protein. He also showed that their plasma triglyceride levels were significantly higher in preeclamptic women with reduced flow-mediated vasodilation. Their plasma adiponectin concentrations correlated negatively with their body mass index. The decrease in plasma adiponectin concentrations is linked with the development of endothelial dysfunction in preeclamptic women.
 This is a prospective cohort which gives a higher level of evidence-based study. Also, gestational weight gain as a risk factor for PIH has not been well researched. Only few studies have examined the association between Institute of Medicine (IOM) guidelines on gestational weight gain and risk associated with development of Pregnancy Induced Hypertension (PIH). To the best of our knowledge, there is no literature on the subject in Nigeria and Africa. Most studies reported in the literatures were mainly on the impact of Hypertensive Disorder of Pregnancy (HDP) on pregnancy outcomes rather than the impact of GWG as a risk factor for the development of PIH.
In our study, pre-pregnancy weight was self-reported which was seen in other similar studies.[21,22] Self-reported pre-pregnancy weight may be subject to recall bias. However, a study by Shin et al showed the validity of self-reported prepregnancy weight and measured weight.[23] Similar study also done by Oken et al showed a correlation of 0.99 between self-reported and measured prepregnancy weight.[24]
The IOM recommendations are mainly from population information from North America, which limits its use in other ethnicities. Most African women generally have a lower BMI prior to pregnancy than those in Westernized societies countries, hence gestational weight gain in pregnancy greater than 12kg was also compared in this study. This is because the IOM classification has not been extensively studied in other ethnicities. However, there are no clear recommendations for BMI and GWG cut-off points among Africans.
Excessive gestational weight gain is associated with development of pregnancy induced hypertension; hence this should be monitored in pregnancy and the women counselled appropriately.

Conclusion

Excessive prepregnancy weight and GWG according to the IOM recommendations are associated with the risk of HDP especially PIH and should therefore be avoided. Assessment risk model using GWG can be used to predict those at risk for PIH in resource poor settings. Women should be counselled against excessive weight prior to conception and need to avoid excessive weight gain in pregnancy. The need to eat healthy with plenty of fruits, exercise and reduction of sugary and excessive calory food should be stressed to our pregnant women.
Studies on larger pregnant population needs to be done to further demonstrate these findings.


 

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	File/Dsecription
	table 1 table 1
	table 2 table 2
	table 3 table 3
	table 4 corrected table 4