Pregnancy and Flatulence
Flatulence is one of the most commonly reported yet least discussed complaints during pregnancy. The good news: it is almost always normal. The less good news: it can be considerable — and biologically completely unavoidable. Behind the increased gas production during pregnancy lie fascinating hormonal, mechanical, and microbiological changes.
Progesterone: The Relaxing Hormone
The pregnancy hormone progesterone rises sharply in early pregnancy and remains elevated until birth. Its primary job is to relax smooth muscle to prevent premature labour. But smooth muscle isn't found only in the uterus — it also forms the walls of the entire gastrointestinal tract. Progesterone therefore slows peristalsis: food and gas move more slowly through the gut. The extended transit time gives intestinal bacteria more time to ferment undigested carbohydrates — and more fermentation means more gas. At the same time, progesterone relaxes the lower esophageal sphincter, which is also responsible for heartburn and increased belching.
Mechanical Pressure: When the Uterus Pushes on the Gut
From the second trimester onwards, the growing uterus begins to physically displace surrounding organs. The intestines, stomach, and liver are pushed upward and to the sides. This mechanical compression further slows gas transit and increases the subjective feeling of fullness and bloating — even if the actual amount of gas hasn't risen dramatically. In the third trimester, when the uterus is at its largest, many pregnant women report a constant feeling of fullness, even after small meals. Eating smaller, more frequent meals can significantly reduce the level of discomfort.
Iron Supplements and Nutritional Supplements
Iron supplements are widely used in pregnancy — and notorious for their effects on the gut. Iron alters the composition of the gut microbiota, slows intestinal transit, and in many women leads to constipation, bloating, and sometimes diarrhoea. Although ferrous iron (Fe²⁺) has higher bioavailability on an empty stomach, it is harder on the stomach. Ferric iron (Fe³⁺) and liposomal iron are often better tolerated. Folic acid supplements and magnesium can also affect bowel activity. Women suffering from severe bloating caused by iron supplements should discuss alternative formulations with their gynaecologist.
Practical Strategies
Since the hormonal causes are unchangeable, relief focuses on what can be influenced: diet and lifestyle. Smaller, more frequent meals reduce the fermentation load at any one time. FODMAP-rich foods such as legumes, onion vegetables, cabbage, and carbonated drinks can be temporarily reduced. Regular, moderate exercise — walking, swimming, prenatal yoga — supports intestinal peristalsis. Adequate fluid intake prevents the slowed transit from leading to constipation. Probiotics show favourable effects in some studies, but the evidence is not yet conclusive. For persistent or severe complaints, always consult your midwife or gynaecologist.
Did you know?
- Progesterone relaxes not just the uterus but the entire gastrointestinal tract — slowing digestion and promoting bloating.
- By the third trimester, the gut is shifted up to 5 cm upward by the pressure of the growing uterus.
- Iron supplements during pregnancy alter the gut microbiota and are one of the most common triggers of digestive complaints.
- Chewing gum and carbonated drinks worsen bloating through additional air swallowing.
Fun Fact
In a British survey of 1,200 pregnant women, 84 percent reported farting significantly more during pregnancy than before — but only 12 percent had discussed it with their gynaecologist or midwife. The topic remains one of the most-searched-for yet least-discussed pregnancy problems.
Sources
- Wald, A. et al. (1982). Effect of pregnancy on gastrointestinal transit. Digestive Diseases and Sciences, 27(11), 1015–1018.
- Parry, E. et al. (1970). Transit time in the small intestine in pregnancy. Journal of Obstetrics and Gynaecology, 77(10), 900–901.
- Bäckström, R. et al. (2018). Iron supplementation alters the gut microbiota in pregnant women. Journal of Nutrition, 148(9), 1399–1408.
- Vazquez, J.C. (2010). Constipation, haemorrhoids, and heartburn in pregnancy. Clinical Evidence, BMJ.