Excessive weight gain during pregnancy is associated with prolonged labor

A study published in the journal PLoS ONE examines the association between excessive weight gain during pregnancy and the subsequent risk of prolonged labor or related complications during childbirth in Japanese women.

Protracted labor is a suboptimal and often dangerous type of labor in which the baby is born very slowly. This condition can lead to labor stopping in the first or second stage and can have serious and long-term consequences for mother and baby, including death.

Although prolonged labor affects only 8% of all pregnant women, its incidence is increasing worldwide and the condition is one of the most common complications of childbirth. Despite decades of research aimed at speeding up labor to minimize clinical harm to the mother and her newborn, few studies have identified risk factors associated with prolonged labor.

Nullity (no previous birth), use of regional anesthesia, older maternal age, high birth weight, shorter maternal height, and excess maternal weight gain may increase the risk of prolonged labor. In particular, excess maternal weight gain has been evaluated in a clinical setting and has been associated with an increased risk of prolonged labor.

Many of these studies used small samples, included biased participant selection, and produced slightly inconsistent results. Moreover, all of the studies on the topic included only American or European women.

Given the potential role of height in the risk of prolonged labour and the significant role of ethnicity in determining height, studies linking ethnic characteristics with maternal weight gain and prolonged labour are needed.

To explore this potential link, the Perinatal Committee of the Japanese Society of Obstetrics and Gynecology (JSOG) recently issued guidelines on acceptable weight gain during pregnancy. According to these guidelines, excessive weight gain was defined as a weight gain of 15, 13, 10, or 5 kg in women with a prepregnancy body mass index (BMI) of less than 18.5 kg/m2, 18.5–25 kg/m2, 25–30 kg/m2, and more than 30.0 kg/m2, respectively. However, these guidelines have never been scientifically tested.

The present study aimed to investigate the association between excessive weight gain and prolonged labor using the new JSOG guidelines. Data were obtained from the Japan Environment and Children Study (JECS), an ongoing Japanese fertility study conducted at 15 regional centers across Japan, including women recruited from January 2011 to March 2014.

Inclusion criteria for the study included women with an expected delivery date after August 2011, with complete obstetric and demographic records. Women who delivered before 37 weeks of gestation, after 42 weeks of gestation, had a cesarean section, or had multiple pregnancies were excluded from the analysis.

Data collected included medical and obstetric records and questionnaires completed by participants in the first, second and third trimesters and postpartum. Weight gain during pregnancy was calculated by comparing maternal weight before pregnancy and seven days before delivery. Confounding variables included obesity, height, large-for-gestational-age (LGA) babies, anesthesia and maternal age.

Of the 104,062 participants in the JECS cohort, 71,154 women met inclusion criteria. The mean maternal age was 30.9 years and the mean BMI was 21.1 kg/m2.

The cohort included 28,442 nulliparous and 42,712 multiparous women. Using JSOG criteria, 15,996 women had excessive gestational weight gain, 82.9% of whom had a prenatal BMI greater than 25 kg/m2.

Gestational age, pre-pregnancy BMI, pre-delivery BMI, maternal height and labour duration were significantly higher in the subgroup with excessive weight gain compared to the group without excessive weight gain. The overall rate of prolonged labour was 10.2%, with a mean labour duration of 12.4 hours compared to 8.5 hours in the normal group. More than 82% of women with prolonged labour had a pre-delivery BMI greater than 25 kg/m2.

Multivariate and Kaplan-Meier analyses found a statistically significant association between excess maternal weight gain during pregnancy and subsequent risk of prolonged labor for both nulliparous and multiparous women, with aOR of 1.21 and 1.15, respectively.

In this nationwide Japanese cohort, excess maternal weight gain was significantly associated with prolonged labor. These findings likely underestimate the true association between the variables assessed because of the large proportion of excluded cesarean sections that would have resulted in prolonged vaginal labor if longer.