May 21, 2018
Existing guidelines for weight gain and loss during pregnancy require adjustment to optimize outcomes in underweight and very obese women, and their babies, shows a large study from the French island of La Reunion.
The authors, led by Pierre-Yves Robillard, MD, from Centre Hospitalier Universitaire Sud Reunion, note that the US Institute of Medicine (IOM) 2009 recommendations are adequate for normal and overweight women, but based on these new findings, are not appropriate for thin and obese women.
Specifically, their analysis of over 52,092 full-term births found that a thin woman (with a body mass index [BMI] of 17 kg/m2) should gain 21.6 kg (48 lbs) during pregnancy (instead of 12.5–18 kg as recommended), obese woman (with a BMI of 32 kg/m2) should gain 3.6 kg (instead of 5–9 kg), and a very obese woman (with a BMI of 40 kg/m2) should actually strive to lose 6 kg (13 lbs).
Knowing the optimal gestational weight gain among the annual 135 million pregnancies worldwide is considered to be one of the holy grails of healthcare, note the authors in their introduction. This observational study goes some way to tackling the lack of consensus regarding the optimal gestational weight gain for different maternal BMI categories.
The results were published in the May issue of Heliyon.
"Women want to know what their optimal weight gain should be to have their baby as safely as possible, and their maternity care providers want to know what advice they can give women throughout their pregnancy," said Robillard in a press release.
Determining Optimal Weight Gain (or Loss) by Pre-pregnancy BMI
The observational study had two key aims: firstly, to determine the maternal BMI range associated with a balanced risk of giving birth to a smaller or larger baby (10% small for gestational age [SGA] newborns, 10% large for gestational age [LGA]); and secondly, to investigate the interaction between maternal pre-pregnancy BMI, gestational weight gain, and neonatal birthweight centiles.
Data were drawn from 16.5 years (2001–2017) of live-birth records at the university's maternity unit. All consecutive singleton live births (37 weeks plus) were included.
To aid the analysis, researchers proposed a term, maternal fetal corpulence symbiosis (MFCS), to describe the point at which women with a normal BMI achieve equilibrium in the risk of SGA-LGA newborns of 10% each way.
The study explored how MFCS shifts with increasing gestational weight gain in 5 kg/m2 BMI increments and pinpointed the optimal weight gain for a balanced risk of having an SGA and LGA baby for each BMI category.
The data showed a point at which the proportions of SGA and LGA newborns were both 10%, which happens naturally for normal-weight women (BMI 20–24 kg/m2).
"This is a surprising finding, because the very definition of SGA (≤ 10th percentile) and LGA (≥ 90th percentile) have never been designed to correspond with maternal BMI...[which] suggests that there is a kind of biological maternal–fetal connection," write the authors.
They found that "the natural tendency for thin women was to spontaneously have some 25% of SGA and 2% of LGA babies, while on the other side of the spectrum, very obese women had spontaneously some 20% of LGA and 5% of SGA newborns (see Figure)."
In addition, Robillard and colleagues point out that, for all women, they noticed a linear association between pre-pregnancy BMI and gestational weight gain from very thin to obese mother categories, which will "greatly facilitate an individualized approach when advising women about their optimal gestational weight gain without needing to put them in fixed categories (such as underweight, normal, overweight, obese, very obese, super obese)."
Formula and Calculator to Estimate Appropriate Weight Gain/Loss
To facilitate estimating the appropriate weight gain/loss that corresponds to the balanced risk of having an SGA or LGA newborn (depending on pre-pregnancy BMI), researchers determined a linear law: opGWG (kg) = -1.2 ppBMI (kg/m2) + 42 ± 2 kg (opGWG: optimal gestational weight gain, ppBMI: maternal pre-pregnancy BMI).
For convenience, they also developed an online calculator, currently available in French, but Robillard told Medscape Medical News he is working on an English version and hopes to provide one in Spanish.
Finally, the authors add that the study findings will "enable maternity care providers and pregnant women to agree on the optimal gestational weight gain. For example, you have a BMI of 17.5 kg/m2 ... you should try to gain 21 kg during this pregnancy, versus your BMI is 33 kg/m2, and you need to try to restrict your weight gain to 2.4 kg."
The authors have reported no relevant financial relationships.