Qn of the Month: Does It Matter What I Weigh Before I Get Pregnant?

A: Ladies, regardless of whether you are underweight or overweight, your pre-pregnancy weight status does matter! It can affect your fertility, increase your risk of poorer birth outcomes compared to those of a normal or healthier weight status going into pregnancy, and also impact your post-partum health.

Firstly, what determines overweight or underweight? According to national and international authoritative bodies like the World Health Organization (WHO) and the United States Centers for Disease Control and Prevention (CDC), weight status is categorized using the Body Mass Index (BMI). Underweight is defined as a BMI less than 18.5, a healthy or ‘normal’ status is 18.5 – 24.9, overweight is defined as a BMI between 25 and 29.9, and obesity as a BMI greater than or equal to 30. Note that BMI is calculated by dividing weight in kilograms by height in meters squared. Obesity status is further subdivided into 3 classes depending on the BMI level of an individual.

From a recent Maternal Nutrition Intensive Course that I attended, the consequences of being overweight or obese in terms of pregnancy outcomes were discussed in detail. These included an increased chance of lower fertility, a lower success of ART (assisted reproductive technology), a tendency for increased likelihood of getting gestational hypertension and pre-eclampsia, as well as gestational diabetes. Obesity prior to pregnancy increased the risk of pre-eclampsia 3 to 8 fold. More alarmingly, if a woman has gestational hypertension and pre-eclampsia during pregnancy, they have double the risk of getting type 2 diabetes in the future. A high pre-pregnancy weight is also associated with more postpartum depression 6-8 weeks after delivery and a greater chance of postpartum weight retention.

A mother’s high pre-pregnancy weight can also affect her newborns in a variety of ways. For instance, during pregnancy, obese women are about twice as likely to need induction of labor, and congenital anomalies are more common in babies born to overweight and obese women. These include neural tube defects like spina bifida (even after controlling for folate intake), cardiac defects and limb reduction. For obese women, the birthweight of full-term infants tend to follow a ‘U’ shaped curve; there is an increased likelihood of either low birthweight or large for gestational age babies. Pre-term birth rates are also higher among obese women. This may be due to mothers having to be medically induced as a necessity due to high blood pressure or diabetes, or due to spontaneous pre-term births as a result of infection or inflammation.   Research is ongoing in this important area.

While a smaller proportion of the population have a prepregnancy underweight status, this is still a cause for concern as such women tend to be at higher risk for having low birth weight (LBW), small for gestational age (SGA), and  preterm infants.

So what is the take home message? For the best health for you and your baby, aim to get to a healthier weight prepregnancy if you are overweight or underweight. This means a BMI as much in the healthy weight range as possible. This can be achieved by eating as much as possible a whole foods plant-based diet and being regularly physically active.


  1. About Adult BMI. Centers for Disease Control and Prevention. https://www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/. Reviewed and updated May 15, 2015. Accessed July 26, 2017.
  2. Gaillard R, Durmuş B, Hofman A, Mackenbach JP, Steegers EA, Jaddoe VW. Risk factors and outcomes of maternal obesity and excessive weight gain during pregnancy. Obesity (Silver Spring). 2013 May;21(5):1046-1055.
  3. Schummers L, Hutcheon JA, Bodnar LM, Lieberman E, Himes KP. Risk of adverse pregnancy outcomes by prepregnancy body mass index: a population-based study to inform prepregnancy weight loss counseling. Obstet Gynecol. 2015 Jan;125(1):133-143. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4285688/. Accessed July 26, 2017.)
  4. Papachatzi E, Dimitriou G, Dimitropoulos K, Vantarakis A. Pre-pregnancy obesity: maternal, neonatal and childhood outcomes. J Neonatal Perinatal Med. 2013;6(3):203-216. DOI: 10.3233/NPM-1370313.
  5. Stothard KJ, Tennant PW, Bell R, Rankin J. Maternal overweight and obesity and the risk of congenital anomalies: a systematic review and meta-analysis. JAMA. 2009 Feb 11;301(6):636-650. doi: 10.1001/jama.2009.113.
  6. Waller DK, Shaw GM, Rasmussen SA, Hobbs CA, Canfield MA, Siega-Riz AM, et al.; National Birth Defects Prevention Study. Prepregnancy obesity as a risk factor for structural birth defects. Arch Pediatr Adolesc Med. 2007 Aug;161(8):745-750.
  7. Carmichael SL, Rasmussen SA, Shaw GM. Prepregnancy obesity: a complex risk factor for selected birth defects. Birth Defects Res A Clin Mol Teratol. 2010 Oct;88(10):804-810.)

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