Why obesity matters before pregnancy
Obesity is defined as severe excess weight, beginning at a BMI of 30 and classified into three stages. All forms of obesity increase the risk of conditions such as high blood pressure, diabetes, breathing difficulties, cardiovascular disease and joint problems.
For women who want to have children, these risks also affect fertility, the course of pregnancy and the health of the baby.
Because of this, women with severe obesity are strongly advised to lose a significant amount of weight before becoming pregnant, ideally returning to a healthy range. Dieting during pregnancy, however, is not safe and can harm the developing baby.
Risks at the beginning of pregnancy
Pregnant women with obesity need close and consistent medical monitoring throughout pregnancy. This is the best way to detect and manage obesity-related complications early.
Routine ultrasound scans are often less reliable, because the signals cannot pass deeply enough through excess abdominal tissue. As a result, certain fetal abnormalities may be detected later or missed entirely.
Another effect is reduced awareness of the baby’s early movements. Women of a healthy weight typically feel movements around the 18th week, while women with obesity often feel them only after the 24th week.
Pregnancy also becomes visible to others much later. A woman of a healthy weight develops a compact, clearly defined bump, whereas in women with obesity the baby has more space within the already enlarged abdomen. This means a pregnancy can go unnoticed for longer.
Other pregnancy-related risks
Women with obesity already face higher health risks, and pregnancy increases many of them. The risk of gestational diabetes is significantly higher due to pre-existing insulin resistance. A glucose tolerance test at 24 to 28 weeks helps detect it early.
They also need frequent monitoring of blood sugar, blood pressure and fetal development. High blood pressure can lead to pre-eclampsia, a condition marked by protein in the urine and, in severe cases, dangerous seizures. If your BMI is 30 or above, your risk of pre-eclampsia is two to four times higher than for a woman with a BMI under 25.
Risks during birth
Women with obesity have a higher likelihood of premature birth or miscarriage. There is also an increased chance of needing a caesarean birth or induced labour.
A higher BMI raises the risk of abnormal fetal heart rate patterns shortly before delivery. It can also increase the chance of the baby’s head being too large for the mother’s birth canal. Overall, the risk of complications during birth is significantly higher.
Long-term impact on the child
Even when a baby is born healthy, the mother’s obesity can have long-term consequences. According to British research, children of mothers with obesity have a much higher risk of developing cardiovascular disease later in life.
These children are also more likely to become severely overweight themselves and to face the same associated health risks.
Prevention and what mothers can do
Women with severe obesity who are pregnant or planning a pregnancy should pay close attention to nutrition alongside regular medical monitoring. The common belief that pregnant women should “eat for two” is not correct.
The focus should be on a balanced, nutrient-rich diet with plenty of vitamins, minerals and fibre, rather than on increasing calorie intake.
There are also three supplements that make a real difference. If your BMI is 30 or above, UK guidelines recommend a higher dose of folic acid (5mg a day), available on prescription, ideally from a month before conception until the 13th week. All pregnant women are advised to take 10 micrograms of vitamin D a day throughout pregnancy and breastfeeding. If you have additional risk factors for pre-eclampsia, your midwife may also recommend a low dose of aspirin from the 12th week until birth.
