Maternal adaptations to pregnancy: Gastrointestinal tract

INTRODUCTION — Pregnancy has little, if any, effect on gastrointestinal secretion or absorption, but it has a major effect on gastrointestinal motility. Pregnancy-related changes in motility are present throughout the gastrointestinal tract and are related to increased levels of progesterone. In addition, the enlarging uterus displaces bowel, which can affect the presentation of disorders such as appendicitis. Knowledge of the gastrointestinal adaptation to pregnancy is necessary for accurate interpretation of laboratory tests as well as imaging studies in the pregnant patient.

This topic will review maternal gastrointestinal tract changes during pregnancy and common gastrointestinal disorders related to pregnancy. Information on maternal adaptations to other organ systems are presented separately.

●(See "Maternal adaptations to pregnancy: Cardiovascular and hemodynamic changes".)

●(See "Maternal adaptations to pregnancy: Musculoskeletal changes and pain".)

●(See "Maternal adaptations to pregnancy: Renal and urinary tract physiology".)

●(See "Maternal adaptations to pregnancy: Dyspnea and other physiologic respiratory changes".)

●(See "Maternal adaptations to pregnancy: Skin and related structures".)

OROPHARYNX — The mucous membrane lining the oropharynx is responsive to the hormonal changes related to pregnancy. The gingiva is primarily affected, while the teeth, tongue, and salivary glands are spared, although excessive salivation during pregnancy (ptyalism) has been described [1-3].

Common oral health conditions that arise during pregnancy include gingivitis, tooth mobility or erosion, oral gingival lesions, and dental caries. Questions to assess oral health in pregnancy can be found in the American College of Obstetricians and Gynecologists Committee Opinion on oral health.

The effect of pregnancy on the initiation or progression of caries is not clear; pregnancy-related changes in the oral environment (salivary pH, oral flora) or in maternal diet and oral hygiene may increase the risk of caries [4]. (See "Maternal adaptations to pregnancy: Skin and related structures", section on 'Mucosa and nonkeratinized epithelium'.)

Taste — Most studies suggest that taste perception changes during pregnancy [5-8]. The etiology is unknown and the direction of taste change varies among studies.

Gingiva — Enlargement and blunting of the interdental papillae of the gingiva may result in gingivitis (picture 1), which is common. (See "Maternal adaptations to pregnancy: Skin and related structures", section on 'Mucosa and nonkeratinized epithelium' and "Overview of gingivitis and periodontitis in adults".)

Pyogenic granuloma of pregnancy — Pyogenic granulomas (also known as lobular capillary hemangioma, pregnancy tumor or epulis, and granuloma gravidarum) are benign, vascular tumors with friable surfaces (picture 2 and picture 3) that develop over a few days to weeks in early pregnancy. The oral mucosa, lip, and tongue are common sites of occurrence. (See "Pyogenic granuloma (lobular capillary hemangioma)" and "Maternal adaptations to pregnancy: Skin and related structures", section on 'Mucosa and nonkeratinized epithelium'.)

Ptyalism or sialorrhea gravidarum — Ptyalism or sialorrhea of pregnancy is an oral pathological condition consisting of excessive salivation that typically begins in the first trimester [2,9]. Symptoms generally abate in the second trimester, although they can continue to term. Salivary volumes range from 1.5 L to 2 L per day [10]. Reported incidences range widely from 0.08 percent to 35 percent and depend upon the definition used (eg, inclusion of patients with pseudo-sialorrhea) [10,11]. The mechanism in pregnancy is not known, and ptyalism is commonly associated with nausea and vomiting as well as hyperemesis gravidarum [2]. (See "Nausea and vomiting of pregnancy: Treatment and outcome".)

Causes of ptyalism unrelated to pregnancy include gastroesophageal reflux, medications (eg, clozapine), or irritants (eg, smoking). For women with a potential identified cause, treatment or removal of the underlying cause reduces excessive salivation [9,10,12]. For women with symptoms resulting only from pregnancy, treatment is mainly aimed at lessening symptoms. Women have reported relief with frequent expectoration, chewing gum or using lozenges, frequent sips of water, and/or antiemetics [2].

"Pseudo"-sialorrhea is caused by failure to swallow saliva that is being secreted at a normal rate. It may be due to dysphagia, neurologic disease, cultural customs, or psychologic disorders.

ESOPHAGUS AND STOMACH — It is not clear whether gastric acid secretion is altered in pregnant women. Gastric emptying is not affected by pregnancy [13-15]. During labor, however, gastric emptying is prolonged if sedative or opiate drugs are administered. A combination of factors related to pregnancy (lower esophageal sphincter incompetence, gastroesophageal reflux, low gastric pH, distortion of the gastric anatomy due to the enlarging uterus), supine position, and analgesia and anesthesia places pregnant women at increased risk of aspiration during labor and delivery.

In contrast to the stomach, transit time is prolonged in the small and large intestine. (See 'Bloating and constipation' below.)

Women with diabetes may have gastroparesis. (See "Diabetic autonomic neuropathy of the gastrointestinal tract".)

Gastroesophageal reflux — Gastroesophageal reflux (GERD, or heartburn) is reported by 40 to 85 percent of women during pregnancy [16]. Most studies report an increasing prevalence of symptoms from the first to the third trimester, with relief postpartum [17,18]. While GERD symptoms can be severe, erosive gastropathy and other complications are rare [19]. GERD tends to recur in subsequent pregnancies, and similarly affects multiparous and nulliparous women [20].

The pathogenesis of GERD during pregnancy involves both mechanical and intrinsic factors that adversely affect lower esophageal sphincter tone. Lower esophageal sphincter pressure is below the lower limits of normal in all trimesters, returning to normal in the postpartum period [21-23]. A study of women during early pregnancy and six weeks after pregnancy termination also demonstrated a reduced response of the sphincter to injections with pentagastrin, edrophonium, and methacholine, or a protein meal [23]. Thus, it appears that pregnancy is associated with both decreased lower esophageal sphincter pressure and inhibition of the adaptive responses of the sphincter.

Animal and human experiments have helped elucidate the effects of female sex hormones on the lower esophageal sphincter. In vivo models (using the opossum) showed a substantial reduction of lower esophageal tone with the administration of both estradiol and progesterone [24]. Whether the decrease in tone was due to estrogen, progesterone, or both is unclear. Some studies suggest that progesterone is the mediator of lower esophageal sphincter muscle relaxation; however, estrogen is likely needed as a primer because estrogen induces the progesterone receptor [25].

The clinical features, diagnosis, and management of GERD in pregnant women and the general population are presented in the following topics:

●(See "Clinical manifestations and diagnosis of gastroesophageal reflux in adults".)

●(See "Medical management of gastroesophageal reflux disease in adults", section on 'Pregnancy and lactation'.)

Aspiration of gastric contents — Pregnant women are predisposed to gastric aspiration due to increased intra-abdominal pressure and relaxation of the lower esophageal sphincter associated with pregnancy. The highest risk period for occurrence of aspiration is during labor or soon after delivery, presumably as a consequence of sedation and assumption of a recumbent position.

Aspiration may also occur as a complication of intubation for general anesthesia for cesarean delivery. Aspiration pneumonia, acute bronchospasm, or the acute respiratory distress syndrome may ensue. (See "Airway management for the pregnant patient" and "Aspiration pneumonia in adults" and "Acute respiratory distress syndrome: Clinical features, diagnosis, and complications in adults".)

Guidelines for oral intake to minimize this risk in laboring women and women undergoing scheduled cesarean delivery are reviewed separately. (See "Preoperative fasting in adults", section on 'Pregnant patients' and "Labor and delivery: Management of the normal first stage", section on 'Oral intake'.)

Nausea and vomiting — Nausea and vomiting are common during pregnancy, with up to 80 percent of pregnant women reporting nausea and up to 50 percent reporting vomiting [26]. Information on nausea and vomiting in pregnancy is presented in detail separately. (See "Nausea and vomiting of pregnancy: Clinical findings and evaluation" and "Nausea and vomiting of pregnancy: Treatment and outcome".)

LIVER

●Position – In late pregnancy, physical examination of the liver is difficult because of the expanding uterus. The enlarging uterus causes a progressive upward displacement of the diaphragm, to a maximum of 4 cm, and the liver is forced up further into the chest as well. A palpable liver is an abnormal finding. On ultrasound examination, the biliary tract is usually normal.

●The prothrombin time is unchanged during pregnancy, and serum fibrinogen increases in late pregnancy. (See "Maternal adaptations to pregnancy: Hematologic changes", section on 'Coagulation and fibrinolysis'.)

●Blood chemistries – Multiple blood chemicals change as a result of pregnancy (table 1).

•Serum albumin levels decrease during the first trimester because of hemodilution, and this decrement becomes more accentuated with advancing gestation.

•Serum total cholesterol and triglyceride concentrations increase markedly [27-29]. Reported ranges vary among studies. In one large series, the 95^th percentile of the distributions in the second and the third trimesters were: total triglyceride 254 and 415 mg/dL (2.87 and 4.68 mmol/L), respectively; total cholesterol 319 and 380 mg/dL (8.24 and 9.83 mmol/L), respectively; LDL-cholesterol 217 and 251 mg/dL (5.61 and 6.48 mmol/L), respectively; and HDL-cholesterol 98 and 95 mg/dL (2.54 and 2.46 mmol/L), respectively [29]. As the increases in total and LDL cholesterol and triglycerides with pregnancy are physiologic, treatment is not indicated. Women who are receiving statin therapy for hypercholesterolemia that predates pregnancy ideally should stop statin treatment three months prior to conception. However, individual decisions need to be made about benefit versus risk in patients at very high risk of a myocardial infarction or stroke, such as those with homozygous familial hypercholesterolemia or established cardiovascular disease [30]. (See "Familial hypercholesterolemia in adults: Treatment", section on 'Fertile women' and "Statins: Actions, side effects, and administration" and "Statins: Actions, side effects, and administration", section on 'Risks in pregnancy and breastfeeding'.)

•Serum alkaline phosphatase concentrations are significantly higher (up to two to four times normal) in the third trimester, primarily due to placental synthesis of alkaline phosphatase.

•Serum gamma-glutamyl transpeptidase is significantly reduced and 5'-nucleotidase is slightly increased.

The other liver biochemical tests are either normal or slightly increased or decreased, but remain within the normal range [31]. Thus, an increase in serum aminotransferase, bilirubin, or fasting total bile acid concentrations during pregnancy may be pathologic and should prompt further evaluation.

Additional issues regarding the effect of pregnancy on the liver and liver disease are discussed separately.

●(See "Approach to evaluating pregnant patients with elevated liver biochemical and function tests".)

●(See "Overview of coincident acute hepatobiliary disease in pregnant women".)

●(See "Intrahepatic cholestasis of pregnancy".)

●(See "Pregnancy in women with pre-existing chronic liver disease".)

●(See "Acute fatty liver of pregnancy".)

GALLBLADDER — Pregnancy decreases gallbladder motility and increases the lithogenicity of bile. On ultrasound examination, fasting gallbladder volume and residual volume after contraction may be increased, with no change in the size of the common hepatic duct [32]. Epidemiologic studies have shown that pregnancy is associated with an increased risk for gallstones. (See "Gallstone diseases in pregnancy".)

PANCREAS — There is a paucity of information on the effect of pregnancy and sex steroid hormones on pancreatic secretion. Amylase levels have been reported to remain in the normal range or be slightly elevated [31,33-35].

Acute pancreatitis during pregnancy is rare. Most cases are associated with gallstones and, like acute cholecystitis, the incidence increases with advancing gestational age [36]. (See "Etiology of acute pancreatitis".)

BOWEL, RECTUM, ANUS — Bowel and anorectal symptoms, such as constipation, incontinence, and hemorrhoids, are common during pregnancy and postpartum [37].

Bloating and constipation — Pregnant women frequently experience abdominal bloating and constipation. Prospective longitudinal studies of pregnant women using Rome II criteria to define constipation reported the prevalence ranged from 16 to 39 percent in each trimester of pregnancy and 6 to 12 weeks postpartum [38,39]. This is higher than the baseline rate of constipation (7 percent [38]) in nonpregnant women of similar age. Using Rome IV criteria, the prevalence of constipation in the second and third trimesters was 44 and 36 percent, respectively (21 percent in nonpregnant controls aged 18 to 44 years); a few days after vaginal and cesarean delivery, the prevalence was 47 and 57 percent, respectively, but subsided within four weeks [40].

Abdominal bloating and constipation during pregnancy are likely caused by hormonal changes that affect small bowel and colonic motility. Increased progesterone concentration plays the major role in decreasing the activity of colonic smooth muscle, but other hormones may be involved. Animal and human studies evaluating gastrointestinal transit during pregnancy, and in relation to hormonal changes during the estrus cycle, support this concept [41-44]. For example, a study that measured gastrointestinal transit time and sex hormone concentrations in 15 women during their third trimester of pregnancy and four to six weeks postpartum found that small bowel transit time was significantly longer during pregnancy when progesterone and estradiol levels were increased compared with the postpartum period when the hormonal levels had fallen [41]. Another study noted that intestinal transit times were prolonged in both the second and third trimesters of pregnancy compared with the first trimester or the postpartum period [42]. A third study showed that progesterone inhibited both the amplitude and frequency of spontaneous colon muscle activity, while estrogen and hydrocortisone had no effect [44].

However, other factors may also contribute to the prolongation in transit time. The plasma concentration of motilin (a stimulatory gastrointestinal hormone) is reduced during pregnancy, possibly because progesterone may inhibit motilin release [45]. In addition, the gravid uterus can cause mechanical impedance to small bowel transit, particularly late in gestation.

Pregnant women also become constipated for the same reasons as the general population. In particular, reduced physical activity may be advised because of pregnancy complications and iron may be prescribed because of iron deficiency; both interventions can promote constipation. (See "Etiology and evaluation of chronic constipation in adults", section on 'Definition of constipation'.)

Management of constipation in general and during pregnancy are reviewed in separate topics. (See "Management of chronic constipation in adults" and "Prenatal care: Patient education, health promotion, and safety of commonly used drugs", section on 'Constipation'.)

Hemorrhoids — Hemorrhoids are varicosities in the anal canal caused by increased local venous pressure. Hemorrhoidal disease is particularly frequent in the last trimester of pregnancy and immediately postpartum: Approximately 30 to 40 percent of pregnant women are affected by hemorrhoidal discomfort. Symptoms include pruritus, discomfort, and/or bleeding. (See "Hemorrhoids: Clinical manifestations and diagnosis".)

Constipation exacerbates these symptoms; therefore, adequate hydration and a diet replete with fiber are advisable. Treatment for relief of symptoms consists of conservative medical management using local application of anti-inflammatory, antipruritic, and local anesthetic preparations. Recurrent and severe hemorrhoids usually require surgical treatment, typically hemorrhoidectomy, which can be performed safely during pregnancy if necessary [46]. (See "Home and office treatment of symptomatic hemorrhoids".)

Incontinence of feces and flatus — Pregnancy appears to be a risk factor for fecal incontinence and increased flatus [47]. (See "Fecal and anal incontinence associated with pregnancy and childbirth: Counseling, evaluation, and management".)

Maternal gut microbiome — The microbiome is a suite of genes provided by microbiota living in and on the body which interacts dynamically with its host and environment and changes its composition markedly over time [48]. The microbiome is now considered to be essential as both a commensal and symbiont integral to immune and metabolic health [49]. Gut bacteria stimulate lymphoid tissue associated with the gut mucosa to produce antibodies to pathogens, and play a role in the expression of Toll-like receptors in the intestines (pattern recognition receptors) that may influence oral tolerance and immune memory [50,51].

The maternal gut microbiome has been shown to change across gestational ages; however, the precise implications on fetal and/or neonatal health have not been elucidated [52]. Initial neonatal microbial exposure likely defines successful trajectories of the gut microbiome [53] Massive bacterial colonization of the newborn gut occurs during labor and vaginal delivery upon exposure to maternal vaginal, fecal, and skin microbiota [54]. Microbial colonization of the newborn gut may ultimately play a role in mucosal gut homeostasis and in the predisposition to chronic inflammation [55]. Because cesarean-born neonates do not experience the same exposure to the maternal microbiome, restoration of normal neonatal colonization iatrogenically (termed vaginal seeding) has been suggested, but is discouraged outside of research studies [56,57].

ROLE OF GASTROENTEROLOGY CONSULTATION — The overwhelming majority of gastrointestinal (GI) changes that occur with pregnancy will resolve with delivery and can be managed with supportive care; however, some pathologic conditions are exacerbated or arise during pregnancy and may require expert consultation from a GI health care expert. Conditions such as gallstone pancreatitis, appendicitis, cholelithiasis with cholecystitis, and acute hepatitis require this consultation. Additionally, refractory nausea with vomiting and persistent inability to tolerate oral intake resulting in malnutrition may require consultation from a GI specialist with expertise regarding enteral and parenteral nutrition. Severe dyspepsia that does not resolve with medical therapy may require upper endoscopy, which can be performed safely by a gastroenterologist and is not contraindicated during pregnancy. Ongoing rectal bleeding in the absence of hemorrhoids or preexisting irritable bowel disease warrants a nonurgent referral to a GI specialist, and colonoscopy may be warranted.

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Acid reflux (gastroesophageal reflux disease) during pregnancy (The Basics)" and "Patient education: Pregnancy symptoms (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Oral cavity – Common oral health conditions that arise during pregnancy, including gingivitis, tooth mobility or erosion, oral gingival lesions, and dental caries, as well as questions to assess oral health can be found in the American College of Obstetricians and Gynecologists Committee Opinion on oral health. Common oral health conditions that arise during pregnancy include gingivitis, tooth mobility or erosion, oral gingival lesions, and dental caries. The gingiva is primarily affected, while the teeth, tongue, and salivary glands are spared, although excessive salivation during pregnancy has been described. (See 'Oropharynx' above.)

●Gastrointestinal reflux – Gastrointestinal reflux is common in pregnancy because of decreased lower esophageal sphincter pressure and inhibition of the adaptive responses of the sphincter. Most studies report an increasing prevalence of symptoms from the first to the third trimester, with relief postpartum. Gastroesophageal reflux tends to recur in subsequent pregnancies, and similarly affects multiparous and nulliparous women. (See 'Gastroesophageal reflux' above.)

●Gastric aspiration – Pregnant women are predisposed to gastric aspiration due to increased intraabdominal pressure and relaxation of the lower esophageal sphincter. They are at highest risk of occurrence during labor or soon after delivery, presumably as a consequence of sedation and assumption of a recumbent position. (See 'Aspiration of gastric contents' above.)

●Liver – Serum aminotransferase, bilirubin, and fasting total bile acid concentrations remain within the normal range during pregnancy. Serum albumin and gamma-glutamyl transpeptidase levels are significantly reduced, whereas lipids and alkaline phosphatase levels are significantly increased. Treatment of elevated lipid levels is generally not indicated during pregnancy and women who are receiving statin therapy for hypercholesterolemia that predates pregnancy ideally should stop statin treatment three months prior to conception, unless they are at very high risk of myocardial infarction or stroke. (See 'Liver' above.)

●Gallbladder – Gallbladder volume and the lithogenicity of bile are increased. (See 'Gallbladder' above.)

●Pancreas –Amylase levels appear to remain in the normal range or be slightly elevated. Acute pancreatitis during pregnancy is rare. (See 'Pancreas' above.)

●Bowel

•Abdominal bloating and constipation during pregnancy are likely caused by hormonal changes (increased progesterone concentration) that reduce small bowel and colonic motility, in addition to the bowel compression caused by the growing uterus. (See 'Bloating and constipation' above.)

•Fecal incontinence and flatus are more common during pregnancy. (See 'Incontinence of feces and flatus' above.)

•Hemorrhoids are common in pregnancy, due to increased local venous pressure and an increased prevalence of constipation. Constipation exacerbates these symptoms; therefore, adequate hydration and a diet replete with fiber are advisable. (See 'Hemorrhoids' above.)

•The maternal gut microbiome is influenced by pregnancy, but the long-term maternal and fetal/neonatal implications have not been elucidated at this time.

●Postpartum resolution – The overwhelming majority of gastrointestinal changes that occur with pregnancy will resolve with delivery and can be managed with supportive care. However, conditions such as gallstone pancreatitis, appendicitis, cholelithiasis with cholecystitis, and acute hepatitis require urgent consultation from a gastrointestinal expert.