I've came across quite a few cases of obese patients who would really like to get pregnant and have read a fair share of pregnancy journey stories on various pregnancy forums. Even though most IVF centres have a 35 BMI cut off line, personally I believe losing weight is a number one priority if you wish to get pregnant and are on the higher side of the BMI. The reason is simple, in order to have a healthy baby, you should be healthy first and to me a BMI of more than 30 is definitely not healthy.
Obesity is associated to a variety of endocrine abnormalities that might lead to chronic anovulation in women. Progesterone on the other hand is an extremely important hormone in supporting the implantation of a fertilized egg in the uterus as well as help maintain a pregnancy by preventing menstruation. To have a successful pregnancy, progesterone levels should maintain high and sustained throughout the pregnancy. Failure to keep progesterone level high will result in miscarriage.
In this study of 30 anovulatory obese patients between 18 and 35 years old without any thyroid disease, researchers found that with the mean weight loss of 9.5 kg, which represents a weight loss of 10.96% from initial body weight, 26 patients (86.6%) resumed spontaneous ovulation (1). The results demonstrated that with a small weight reduction and a decrease in total body fat percentage, it will improve the hormonal profile and restore ovulation in anovulatory obese women. Thus weight loss should be considered before starting with ovulation induction therapy.
In a more recent study in Singapore, researchers investigated the association between maternal body mass index (BMI) and serum progesterone level in first trimester singleton pregnancies for 194 women at a tertiary maternity hospital in Singapore, from January 2012 to February 2014. Obesity (maternal BMI ≥30 kg/m2) has an increased risk for serum progesterone <35 nmol/L. Results indicate that maternal obesity is associated with low first trimester serum progesterone.
In conclusion, pre-pregnancy weight optimization is beneficial in regulation of serum progesterone level and maintenance of healthy pregnancy.
1: Hernández García IA, Gutiérrez Gutiérrez AM, Gallardo Lozano E. [Effect of weight reduction on the clinical and hormonal condition of obese anovulatory women]. Ginecol Obstet Mex. 1999 Sep;67:433-7. Spanish. PubMed PMID: 10544539.
2. Goh JY, He S, Allen JC, Malhotra R, Tan TC. Maternal obesity is associated with a low serum progesterone level in early pregnancy. Horm Mol Biol Clin Investig. 2016 Jan 9. pii:/j/hmbci.ahead-of-print/hmbci-2015-0030/hmbci-2015-0030.xml. doi:10.1515/hmbci-2015-0030. [Epub ahead of print] PubMed PMID: 26751901
Dr Nicole Ng (MBBS) is a medical doctor with a passion in women's health and medical research