Men with obesity are at greater risk of impaired sperm production, erectile dysfunction and poor libido.
Women with obesity are at a greater risk of irregular ovulation and other changes to the occytes and endometrium which may reduce the chance of pregnancy.
Guidelines for weight gain in pregnancy aim to balance risks of maternal obesity with the need for optimal fetal nutrition.
Women with obesity should give birth in health care settings with appropriate facilities and experienced health care staff
This page has been written by Dr Sarah Price; and reviewed by Dr Jade Eccles-Smith.
Obesity and the risk of infertility
Women with obesity are more likely to suffer infertility than women of normal weight.1 Obesity is also associated with a prolonged time to pregnancy.2 The mechanisms by which obesity alters female fertility are multi-factorial and include irregular or absence of ovulation, poor quality oocytes, endometrial complications and hormonal changes.345
The median time to pregnancy in women of normal weight is around three months and around five months in women with obesity.6 Hence, in women who can conceive spontaneously, obesity increases the median time to conception by approximately two months. In women who require assisted reproductive treatment to achieve pregnancy, the rate of clinical pregnancy and live birth is lower in women with obesity compared with women of normal weight.78
Male fertility is also impacted by obesity. Men with obesity are at greater risk of suffering from impaired spermatogenesis, reduced circulating testosterone levels, erectile dysfunction and poor libido.9
Risks of obesity in pregnancy and in the post-partum period
The short-term impacts of maternal obesity on pregnancy outcomes have been well described in the medical literature.10 Maternal risks include:
- increased risks of miscarriage11
- gestational diabetes12
- gestational hypertension and pre-eclampsia1213
- induced labour14
- caesarean section15
- anaesthetic complications and wound infections.10
Mothers with obesity are less likely to initiate and maintain breastfeeding.16
Neonatal risks of maternal obesity include large-for-gestational age (‘obesity in the neonate’), jaundice and hypoglycaemia at birth.10 Maternal obesity also results in a small increased risk of congenital anomalies,17 especially congenital heart disease and neural tube defects, and increases the risk of preterm delivery (< 37 weeks’ gestation). Although the overall risk of neonatal death is small, this is increased in the offspring of women with obesity compared to the normal weight population.18
Given the clear link between obesity and adverse pregnancy outcomes, it is reasonable to expect that clinicians should discuss the risk of obesity on the pregnancy. The clinician may also discuss realistic pre-pregnancy weight loss targets and potential consequences of the various weight loss strategies, as discussed below.
Pre-pregnancy weight loss options
1. Lifestyle modification
Lifestyle modification refers to setting weight loss goals and making changes to diet and physical activity. International guidelines for the management of obesity in pregnancy recommend that women try to achieve a ‘healthy’ weight prior to pregnancy. This is variably defined as a BMI of 18.5–24.9 kg/m2, BMI < 35 kg/m2 or a loss of 5–7% of body weight.19 Importantly, clinical trials show that weight loss due to lifestyle modification is usually modest (3–6 kg)20 and this may not be consistent with the degree of weight loss advised by international organisations. For example, for a woman of standard height (162 cm) with a BMI of 40 kg/m2, targeting a ‘healthy’ BMI of 35 kg/m2 equates to a weight loss of 13 kg. This is 2–4 times greater than the modest weight loss achieved in clinical trials using lifestyle modification. A reasonable approach is to aim for 5–7% body weight loss.21 The duration of active weight loss should be short given that longer weight loss attempts do not result in greater weight loss.22
2. Other non-surgical treatment options
With the exception of a few small studies, there is limited experience with the use of pharmacotherapy in the pre-pregnancy setting. The exception is metformin which may improve fertility via an effect unrelated to weight loss.2324 Very Low Energy Diets (VLED) cause weight loss by restriction of calories as well as carbohydrate intake, which then causes fat to be used as a source of energy.25 The resulting ketosis is associated with transient appetite suppression which may facilitate weight loss.26 Although VLED programs may be used in the pre-pregnancy setting, there is currently insufficient evidence to support the routine use of such programs.27
3. Bariatric surgery
Bariatric surgery results in a greater mean weight loss than lifestyle modification. There is good evidence that bariatric surgery prior to pregnancy in women with obesity reduces the rates of gestational diabetes and gestational hypertension/pre-eclampsia.28 29 30 31 32 33 However, the impact of substantial weight loss on the fetal outcomes is less clear. There is some evidence to suggest that there is an increase in the rate of small-for-gestational-age offspring and possible increase in neonatal death after bariatric surgery.30 According to Australian34 35 and American36 guidelines, women who are considering bariatric surgery should wait at least 12 to 24 months post-surgery before attempting to conceive. Women who have had bariatric surgery should also remain under the care of a dietitian to ensure adequate intake of protein and micronutrients in the months prior to conception.36 37 38
Regardless of the method of weight loss, women with obesity should aim for a period of weight maintenance prior to conception in order to ensure the growing fetus is not exposed to any nutritional deficiencies.21 In addition, women with obesity should take high dose folate (5 mg orally daily) and a multivitamin containing iodine for 3 months pre-conception until 12 weeks’ gestation.21 39
During pregnancy: recommended gestational weight gain
Pre-pregnancy weight management should occur in conjunction with appropriate weight management during pregnancy. Catalano et al. has shown that even when women with obesity gain inadequate weight during pregnancy (< 5 kg), they have a significantly increased risk of small-for-gestational-age infants.40 These infants carry the same long-term metabolic risks as large-for-gestational-age infants.41 Women should therefore be supported to gain weight during pregnancy.36 The guidelines for weight gain in pregnancy aim to balance the risks of insufficient weight gain in pregnancy with the risks posed by maternal obesity.42
Recommended gestational weight gain based on pre-pregnancy BMI
American College of Obstetrics and Gynaecology Committee Opinion no. 548: Weight gain during pregnancy, 2013
|Pre-pregnancy weight category||Pre-pregnancy BMI (kg/m2)||Recommended gestational weight gain (kg)||Recommended weight gain in 2nd & 3rd trimester (kg/week)|
|Underweight||< 18.5||12.5–18.0||0.51 (0.44–0.58)|
|Normal weight||18.5–24.9||11.5–16.0||0.42 (0.35–0.50)|
|Obese (all classes)||> 30.0||5.0–9.0||0.22 (0.17–0.27)|
Recommendations for pregnancy and delivery
Maternity care facilities should have well-defined pathways for the care and management of pregnant women with obesity. In some cases, this may mean that a women needs to be transferred to an alternative hospital that has appropriately experienced health care staff and bariatric equipment to care for pregnant women.43
Women with obesity and their offspring have increased risks of congenital abnormalities, fetal growth restriction and macrosomia. Ultrasound assessment is less accurate in women with obesity than women of normal weight, but may be superior to clinical assessment.44 A third trimester fetal growth ultrasound should be offered to all women with obesity.45
There is no universal consensus on the optimum timing of birth for women with obesity in the absence of comorbidities. Awaiting spontaneous labour after the due date may increase the risk of macrosomia and term stillbirth but induction of labour carries the risks of failed induction of labour resulting in emergency Caesarean section.43 Current evidence suggests that delivery by 40 weeks’ gestation significantly reduces the risk of Caesarean section in women with obesity.46
Women who are obese prior to pregnancy are more likely to gain excessive weight in pregnancy and to maintain this additional weight in the long term. Women with obesity should aim to return to their pre-pregnancy weight within 12–18 months of delivery.47
Children born to women with obesity also have an increased risk of obesity compared to children born to normal weight mothers. Childhood obesity is the most significant risk factor for obesity in adulthood.48 49 Therefore, parents should be aware of this association and adopt appropriate lifestyle habits to mitigate against the risk of childhood obesity.