BMI is a measurement used to classify a person’s weight. It is calculated by dividing the person’s weight in kilogram by his/her height in meters squared.
Please note that BMI does not apply to children, elderly, pregnant women and muscular people (athletic).
Women, who are underweight, may suffer from absent periods (amenorrhoea) and are at an increased risk during pregnancy if conception does occur, including: an increased risk of miscarriage, preterm delivery and small for date baby. An underweight woman may benefit from consulting a dietician and receiving psychological support.
Obesity has increased sharply in both developed and developing countries over the past decades with approximately, one third of adults and one sixth of children and adolescents in the USA are obese. Women, who are obese, have up to half the chance of conceiving. Recently, polotsky and colleagues reported that adolescent obesity was related to a four fold increased risk of lifetime no pregnancy and to a three fold increased lifetime risk of having no live birth. It has also been demonstrated that a longer time to pregnancy in obees women compared to normal weight controls. The exact mechanism for the reduced fertility in obese women is not fully understood but ovulation dysfunction is a major factor. Other factors which could play a part include adverse effects on egg, embryo and endometrial receptivity.
If obese women need IVF treatment they will require higher doses of the fertility drugs and require longer duration to achieve follicular development, higher cancellation rates and have reduced conception rates. Furthermore, the miscarriage rates appear to be higher with increasing maternal weight. Also there is an increased risk of developing gestational diabetes, pre-eclampsia and high blood pressure as well as problems during delivery such as an increased risk of shoulder dystocia, caesarean section, postpartum haemorrhage, stillbirth, congenital anomalies, developing blood clot, heart problems and wound infection. They are also more likely to require a general anaesthetic for a caesarean section due to problems sitting an epidural/spinal anaesthetic. In the latest “Saving Mother’s Lives” report (CEMACH, UK. 2007) 28% of women who died had a BMI greater than 30. Recent USA study published in 2015 reported that obesity nearly doubles risk of stillbirth.
Paterson and colleagues in 2011 reported that increased female and male BMI, both independently and in combination negatively affected the live birth rates after IVF. Obesity also has an adverse effect on male infertility and long-term health.
There is evidence that infants of women who are obese are at increased risk of being overweight, have an increased risk of birth defects such as neural tube defects and congenital heart disease and stillbirth etc. A recent study (BMJ 2013) reported that children of obese and overweight women have a higher risk of early cardiovascular death as adults.
Health professionals should appreciate the difficulties faced by many overweight women and men who are struggling with both infertility and are attempting to loose weight. Weight reduction before natural conception or IVF treatment is the best measure to improve pregnancy outcomes in obese women. Weight reduction is best achieved by enrolling on a weight loss programme encompassing dietary advice, exercise and psychological support. The use of drugs to reduce weight may cause side effects with little weight loss and rapid regain after discontinuation. Furthermore that are not recommended to be used around conception. Bariatric surgery such as gastric band should be considered as a last line treatment for weight loss.