How Your Body Changes in Pregnancy: The Digestive System

In previous installments of this series, we have looked at how pregnancy changes the physiology of the respiratory system, the circulatory system, and the urinary system. Today, we’ll explore the digestive system and how it changes in pregnancy. The digestive system is basically a long tube, running from the mouth to the anus, getting narrower and wider at certain spots, with some additional organs —the liver, pancreas, and gallbladder— processing, storing, and/or delivering substances into the tube. From your mouth, food passes through the esophagus, stomach, small intestine, large intestine (also called the colon), the end of which, the rectum, leads to the anus.

During pregnancy, there are a few phenomena causing changes in the function of the digestive system. First, your caloric requirements increase, because you must nourish the growing embryo/fetus, so you take in moderately higher amounts of food than when you’re not pregnant. Next, as the uterus grows within your abdominopelvic cavity, there is increasing pressure on your digestive organs, as pregnancy progresses. Additionally, pregnancy entails dramatic hormonal changes and the digestive system is affected notably.

Hormones affect your digestive system throughout pregnancy and consequently the effects begin early than the effects of the growing womb. Overall, the hormonal changes slow down the movement of food through the gastrointestinal tract, the segment of the long tube of the digestive system that begins with the stomach and ends with the rectum, the final part of the colon. This slowing gives extra time for the absorption of nutrients from the small intestine, but it can lead, or exacerbate constipation, which is further exacerbated as the womb grows pressure on various parts of the intestines. Related to increased constipation, irritable bowel syndrome (IBS) also can emerge or worsen during pregnancy. Abnormalities provoking IBS also include intolerance to certain types of carbohydrates, often due to a deficiency of the enzymes needed to break down the particular substance. The abnormalities also include anxiety and similar behavioral disorders that make nervousness a trigger for an IBS attack. In all cases, IBS is characterized by abdominal pain and altered, or unpredictable bowel habits, including diarrhea and constipation.

The tendency of food to remain longer in the stomach before emptying to the small intestine, and then to remain longer in the small intestine also provokes nausea and vomiting, which also is affected directly by hormones. Nausea and vomiting is very common in pregnancy and usually abates during the latter half of pregnancy. However, a small number of pregnant women suffer from a more serious condition called hyperemesis gravidarum (HG), featuring severe nausea and vomiting, as well as weight loss, and disruption of electrolytes, often with dehydration. It is not the same thing as the normal nausea and vomiting of pregnancy and is related to problems in the liver. Women suffering from HG can develop deficiencies of nutrients such as vitamin B1 (thiamine). In some cases, HG can lead to a severe brain abnormality called Wernicke encephalopathy, featuring tiredness and and confusion, dampened reflexes, problems with movement, including movement of the eyes. In very extreme cases, Wernicke encephalopathy can be fatal, but if recognized early it is easily treated with thiamine . HG also can lead to deficiencies of fat soluble vitamins, such as vitamin K, which is important for blood clotting, so deficiency can lead to bleeding during pregnancy, and severe bleeding during labor and delivery. The vomiting may lead to a particular type of acid-base disturbance called metabolic alkalosis, which turn causes or exacerbates a particular electrolyte disturbance called hypokalemia, low potassium. This can lead to muscle damage, kidney problems, and problems with the rhythm of the heart, which also can be fatal. Excessive vomiting and retching furthermore can damage the esophagus, badly enough to cause bleeding and entry of air into tissues of and behind the chest.

Additional pregnancy complications related to the liver include HELLP, which stands for Hemolysis (breakdown of red blood cells), Elevated Liver enzymes (concentrations in the blood of enzymes from the liver are too high), and Low Platelet count (the number of blood clotting cells –platelets– in the blood is too low). HELLP is life threatening and in some cases can occur as further complication of another pregnancy condition called preeclampsia, but the relationship between HELLP and preeclampsia is controversial. Many cases of HELLP develop in women who do not have preeclampsia, and preeclampsia and HELLP tend to strike mothers-to-be of different age groups, so many researchers consider HELLP and preeclampsia to be a separate conditions. Another liver condition of pregnancy is called fatty liver of pregnancy (AFLP), which tends to occur during the third trimester, usually between 28-40 weeks gestation, and especially weeks 35-36. It also can occur in a mother soon after delivering a baby. In AFLP features high levels of fat accumulated in the mother’s liver. Normally, fat comprises about 5 percent of the liver’s content, but in AFLP the liver consists of 13- 19 percent fat, and this may be due to problems in the rearrangement and breakdown of molecules called fatty acids coming from the fetus.

The gallbladder is also affected noticeably in pregnancy. Just as the hormonal state slows the movement of substances through the gastrointestinal tract, the gallbladder also slows down. Thus, rather than leaving the gallbladder, bile (which is produced by the liver and stored in the gallbladder) tends to remain in the gallbladder and moveout very slowly. This encourages the growth of gallstones, cholelithiasis. During pregnancy, but more so over time after pregnancy, the stones can cause problems by blocking the various ducts through which bile moves. Depending on the location of the obstruction, this can cause inflammation of the gallbladder (cholecystitis) or inflammation of the bile duct system cholangitis. Because each pregnancy give gallstones more opportunity to develop and grow, a high number of pregnancies entails an elevated risk of gallstone disease, which in many cases can reach a point requiring surgery. Additional risk factors include being over the age of forty, being overweight or obese, being native American or Mexican American, and having gallstone disease in your family.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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