Merck Manual

Please confirm that you are a health care professional

honeypot link

Risk Factors for Complications During Pregnancy

By

Raul Artal-Mittelmark

, MD, Saint Louis University School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
Click here for Patient Education
Topic Resources

Risk factors for complications during pregnancy include

Hypertension

Chronic hypertension is differentiated from gestational hypertension, which develops after 20 weeks of pregnancy. In either case, hypertension is defined as systolic BP > 140 mm Hg or diastolic BP > 90 mm Hg on 2 occasions > 24 hours apart.

Hypertension increases risk of the following:

Before attempting to conceive, women with hypertension should be counseled about the risks of pregnancy. If they become pregnant, prenatal care begins as early as possible. Management of hypertension during pregnancy Treatment Recommendations regarding classification, diagnosis, and management of hypertensive disorders (including preeclampsia) are available from the American College of Obstetricians and Gynecologists... read more includes measurements of baseline renal function (eg, serum creatinine, blood urea nitrogen [BUN]), funduscopic examination, and directed cardiovascular evaluation (auscultation and sometimes ECG, echocardiography, or both). Each trimester, 24-hour urine protein, serum uric acid, serum creatinine, and hematocrit are measured. Ultrasonography to monitor fetal growth is done at 28 weeks and every 4 weeks thereafter. Delayed growth is evaluated with multivessel Doppler testing by a maternal-fetal medicine specialist. If women are at high risk of preeclampsia, clinicians should prescribe low-dose aspirin (81 mg orally once a day) to be taken daily starting at 12 to 28 weeks of gestation and taken until delivery (1 Hypertension reference Risk factors for complications during pregnancy include Preexisting maternal disorders Physical and social characteristics (eg, age) Problems in previous pregnancies (eg, spontaneous abortions)... read more Hypertension reference ).

Women with a history of preeclampsia or gestational hypertension are at a higher lifetime risk of cardiovascular events and, after delivery, should be referred for appropriate cardiovascular risk assessment and follow-up.

Hypertension reference

  • 1. ACOG Committee Opinion No. 743: Low-dose aspirin use during pregnancy. Obstet Gynecol 132 (1):e44–e52, 2018. doi: 10.1097/AOG.0000000000002708.

Diabetes

Preexisting insulin-dependent diabetes increases the risk of the following:

The incidence of fetal macrosomia is about 50% higher in pregnant women with preexisting diabetes than in pregnant women in the general population. The incidence of perinatal mortality is also higher.

Tight glucose control before conception is essential to prevent fetal malformations.

Insulin requirements usually increase during pregnancy.

Gestational diabetes increases the risk of the following:

Gestational diabetes is routinely screened for at 24 to 28 weeks and, if women have risk factors, during the 1st trimester. Risk factors include the following:

  • Previous gestational diabetes

  • A macrosomic infant in a previous pregnancy

  • Family history of non-insulin–dependent diabetes

  • Unexplained fetal losses

  • Body mass index (BMI) > 30 kg/m2

  • Certain ethnicities (eg, Mexican Americans, American Indians, Asians, Pacific Islanders) in whom diabetes is prevalent

Some practitioners first do a random plasma glucose test to check whether gestational diabetes is possible. However, screening and confirmation of the diagnosis of gestational diabetes is best based on results of the oral glucose tolerance test (OGTT—see table Glucose Thresholds for Gestational Diabetes Mellitus Using a 3-hour Oral Glucose Tolerance Test Glucose Thresholds for Gestational Diabetes Using a 3-hour Oral Glucose Tolerance Test* Risk factors for complications during pregnancy include Preexisting maternal disorders Physical and social characteristics (eg, age) Problems in previous pregnancies (eg, spontaneous abortions)... read more Glucose Thresholds for Gestational Diabetes Using a 3-hour Oral Glucose Tolerance Test* ). Based on a recommendation from the 2013 National Institutes of Health (NIH) consensus development conference, screening begins with a 1-hour 50-g glucose load test (GLT); if results are positive (plasma glucose > 130 to 140 mg/dL [7.2 to 7.8 mmol/L]), a 3-hour 100-g OGTT is done.

Table
icon

Optimal treatment of gestational diabetes Treatment Pregnancy aggravates preexisting type 1 (insulin-dependent) and type 2 (non–insulin-dependent) diabetes but does not appear to exacerbate diabetic retinopathy, nephropathy, or neuropathy (1)... read more (with dietary modification, exercise, and close monitoring of blood glucose levels and insulin when necessary) reduces risk of adverse maternal, fetal, and neonatal outcomes. Women with gestational diabetes are at a higher lifetime risk of cardiovascular events and, after delivery, should be referred for appropriate cardiovascular risk assessment and follow-up.

Table
icon

Women with gestational diabetes mellitus may have had undiagnosed diabetes mellitus before pregnancy. Thus, they should be screened for diabetes mellitus Screening for disease Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more 6 to 12 weeks postpartum, using the same testing and criteria used for patients who are not pregnant.

Diabetes references

  • 1. Artal R: Exercise: The alternative therapeutic intervention for gestational diabetes. Clinical Obstetrics and Gynecology 46 (2):479–487, 2003.

  • 2. Artal R: The role of exercise in reducing the risks of gestational diabetes mellitus in obese women. Best Pract Res Clin Obstet Gynaecol 29 (1):123–4132, 2015.

Sexually Transmitted Diseases (STDs)

Without treatment, risk of transmission of HIV Transmission Human immunodeficiency virus (HIV) infection results from 1 of 2 similar retroviruses (HIV-1 and HIV-2) that destroy CD4+ lymphocytes and impair cell-mediated immunity, increasing risk of certain... read more Transmission from woman to offspring is about 30% prepartum and about 25% intrapartum. Neonates are given antiretroviral treatment within 6 hours of birth to minimize risk of transmission intrapartum.

Routine prenatal care includes screening tests for HIV infection, hepatitis B, and syphilis and, if < 25 years, for chlamydial infection and gonorrhea at the first prenatal visit. Syphilis testing is repeated during pregnancy if risk continues and at delivery for all women. Pregnant women who have any of these infections are treated with antimicrobials.

Treatment of bacterial vaginosis, gonorrhea, or chlamydial infection may prolong the interval from rupture of the membranes to delivery and may improve fetal outcome by decreasing fetal inflammation.

Zidovudine or nevirapine is given to pregnant women with HIV infection. This treatment reduces risk of HIV transmission to the fetus Prevention Human immunodeficiency virus (HIV) infection is caused by the retrovirus HIV-1 (and less commonly by the related retrovirus HIV-2). Infection leads to progressive immunologic deterioration and... read more Prevention by two thirds; risk is probably lower (< 2%) with a combination of 2 or 3 antivirals. These drugs are recommended despite potential toxic effects in the fetus and woman.

Pyelonephritis

During pregnancy, recurrent bacteriuria occurs more frequently, and the incidence of pyelonephritis is higher. If bacteruria is present, 20 to 35 % of pregnant women develop a urinary tract infection (UTI), and pyelonephritis is possible.

Pyelonephritis is the most common nonobstetric cause of hospitalization during pregnancy.

Pregnant women with pyelonephritis are hospitalized for evaluation and treatment, primarily with urine culture plus sensitivities, IV antibiotics (eg, a 3rd-generation cephalosporin with or without an aminoglycoside), antipyretics, and hydration. Oral antibiotics specific to the causative organism are begun 24 to 48 hours after fever resolves and continued to complete the whole course of antibiotic therapy, usually 7 to 10 days.

Prophylactic antibiotics (eg, nitrofurantoin, trimethoprim/sulfamethoxazole) with periodic urine cultures are continued for the rest of the pregnancy.

Acute Surgical Problems

Major surgery, particularly intra-abdominal, increases risk of the following:

However, surgery is usually tolerated well by pregnant women and the fetus when appropriate supportive care and anesthesia (maintaining blood pressure and oxygenation at normal levels) are provided, so physicians should not be reluctant to operate; delaying treatment of an abdominal emergency is far more dangerous.

After surgery, antibiotics and tocolytic drugs are given for 12 to 24 hours.

If nonemergency surgery is necessary during pregnancy, it is most safely done during the 2nd trimester.

Genital Tract Abnormalities

Structural abnormalities of the uterus and cervix (eg, uterine septum, bicornuate uterus) make the following more likely:

Cervical insufficiency Cervical Insufficiency Cervical insufficiency (formerly called cervical incompetence) is painless cervical dilation resulting in delivery of a live fetus during the 2nd trimester. Transvaginal cervical ultrasonography... read more Cervical Insufficiency (incompetence) makes preterm delivery more likely. The risk of cervical insufficiency is higher in women who have had lacerations or injury of the cervix during a previous procedure (eg, therapeutic abortion, instrumental vaginal deliveries). Cervical insufficiency can be treated with surgical intervention (cerclage), vaginal progesterone, or sometimes a vaginal pessary.

If, before pregnancy, women have had a myomectomy in which the uterine cavity was entered, cesarean delivery is required because uterine rupture Uterine Rupture Uterine rupture is spontaneous tearing of the uterus that may result in the fetus being expelled into the peritoneal cavity. Uterine rupture is rare. It can occur during late pregnancy or active... read more is a risk during subsequent vaginal delivery.

Uterine abnormalities that lead to poor obstetric outcomes often require surgical correction, which is done after delivery.

Maternal Age

In women > 35, the incidence of preeclampsia is increased, as is that of gestational diabetes Pregnancy aggravates preexisting type 1 (insulin-dependent) and type 2 (non–insulin-dependent) diabetes but does not appear to exacerbate diabetic retinopathy, nephropathy, or neuropathy (1)... read more , dysfunctional labor Protracted labor is abnormally slow cervical dilation or fetal descent during active labor. Diagnosis is clinical. Treatment is with oxytocin, operative vaginal delivery, or cesarean delivery... read more , abruptio placentae Abruptio Placentae Abruptio placentae is premature separation of a normally implanted placenta from the uterus, usually after 20 weeks gestation. It can be an obstetric emergency. Manifestations may include vaginal... read more , stillbirth Stillbirth Stillbirth is delivery of a dead fetus at > 20 weeks gestation. Maternal and fetal testing is done to determine the cause. Management is as for routine care after live delivery. Stillbirth,... read more , and placenta previa Placenta Previa Placenta previa is implantation of the placenta over or near the internal os of the cervix. Typically, painless vaginal bleeding with bright red blood occurs after 20 weeks gestation. Diagnosis... read more . These women are also more likely to have preexisting disorders (eg, chronic hypertension Hypertension Hypertension is sustained elevation of resting systolic blood pressure (≥ 130 mm Hg), diastolic blood pressure (≥ 80 mm Hg), or both. Hypertension with no known cause (primary; formerly, essential... read more Hypertension , diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more ). Because risk of fetal chromosomal abnormalities Overview of Chromosomal Anomalies Chromosomal anomalies cause various disorders. Anomalies that affect autosomes (the 22 paired chromosomes that are alike in males and females) are more common than those that affect sex chromosomes... read more increases as maternal age increases, genetic testing Genetic Evaluation Genetic evaluation is part of routine prenatal care and is ideally done before conception. The extent of genetic evaluation a woman chooses is related to how the woman weighs factors such as... read more Genetic Evaluation should be offered.

Maternal Weight

Pregnant women whose body mass index (BMI) was < 19.8 kg/m2 before pregnancy are considered underweight, which predisposes to low birth weight (< 2.5 kg) in neonates. Such women are encouraged to gain at least 12.5 kg during pregnancy.

Pregnant women whose BMI was 25 to 29.9 kg/m2 (overweight) or ≥ 30 kg/m2 (obese) before pregnancy are at risk of maternal hypertension Hypertension in Pregnancy Recommendations regarding classification, diagnosis, and management of hypertensive disorders (including preeclampsia) are available from the American College of Obstetricians and Gynecologists... read more and diabetes Diabetes Mellitus in Pregnancy Pregnancy aggravates preexisting type 1 (insulin-dependent) and type 2 (non–insulin-dependent) diabetes but does not appear to exacerbate diabetic retinopathy, nephropathy, or neuropathy (1)... read more , postterm pregnancy Postterm Pregnancy Postterm pregnancy refers to gestation that lasts ≥ 42 (> 41 6/7) weeks. Late-term pregnancy is defined as 41 0/7 to 41 6/7 weeks. Antenatal surveillance should be considered at 41 weeks. Induction... read more , pregnancy loss Spontaneous Abortion Spontaneous abortion is noninduced embryonic or fetal death or passage of products of conception before 20 weeks gestation. Threatened abortion is vaginal bleeding without cervical dilation... read more , fetal macrosomia Large-for-Gestational-Age (LGA) Infant Infants whose weight is > the 90th percentile for gestational age are classified as large for gestational age. Macrosomia is birthweight > 4000 g in a term infant. The predominant cause is maternal... read more , congenital malformations, intrauterine growth restriction Small-for-Gestational-Age (SGA) Infant Infants whose weight is the 10th percentile for gestational age are classified as small for gestational age. Complications include perinatal asphyxia, meconium aspiration, polycythemia, and... read more , preeclampsia Preeclampsia and Eclampsia Preeclampsia is new-onset or worsening of existing hypertension with proteinuria after 20 weeks gestation. Eclampsia is unexplained generalized seizures in patients with preeclampsia. Diagnosis... read more , and the need for cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. Up to 30% of deliveries in the US are cesarean. The rate of cesarean delivery fluctuates. It has recently increased, partly... read more . Ideally, weight loss should begin before pregnancy, first by trying lifestyle modifications (eg, increased physical activity, dietary changes). Women who are overweight or obese are encouraged to limit weight gain during pregnancy, ideally by modifying their lifestyle. The Institute of Medicine (IOM) uses the following guidelines:

  • Overweight: Weight gain limited to < 6.8 to 11.3 kg (< 15 to 25 lb)

  • Obese: Weight gain limited to < 5 to 9.1 kg (< 11 to 20 lb)

However, not all experts agree with IOM recommendations. Many experts recommend an individualized approach that can include more limited weight gain plus lifestyle modifications (eg, increased physical activity, dietary changes), particularly for obese women (1 Maternal weight references Risk factors for complications during pregnancy include Preexisting maternal disorders Physical and social characteristics (eg, age) Problems in previous pregnancies (eg, spontaneous abortions)... read more Maternal weight references ). During pregnancy, most women should be encouraged to exercise at least 3 times a week for a total of 150 minutes each week (2 Maternal weight references Risk factors for complications during pregnancy include Preexisting maternal disorders Physical and social characteristics (eg, age) Problems in previous pregnancies (eg, spontaneous abortions)... read more Maternal weight references ).

For overweight and obese pregnant women, lifestyle modifications during pregnancy reduce the risk of gestational diabetes and preeclampsia.

Discussing appropriate weight gain, diet, and exercise at the initial visit and periodically throughout the pregnancy is important. The 2016 ACOG (American College of Obstetricians and Gynecologists) obesity toolkit is a helpful resource for managing overweight and obesity.

Maternal weight references

  • 1. Artal R, Lockwood CJ, Brown HL: Weight gain recommendations in pregnancy and the obesity epidemic. Obstet Gynecol 115 (1):152–155, 2010. doi: 10.1097/AOG.0b013e3181c51908

  • 2. Mottola MF, Davenport MH, Ruchat SM, et al: 2019 Canadian guideline for physical activity throughout pregnancy. Br J Sports Med 52 (21):1339–1346, 2018. doi: 10.1136/bjsports-2018-100056

Maternal Height

Exposure to Teratogens

Common teratogens (agents that cause fetal malformation) include infections, drugs, and physical agents. Malformations are most likely to result if exposure occurs between the 2nd and 8th week after conception (the 4th to 10th week after the last menstrual period), when organs are forming. Other adverse pregnancy outcomes are also more likely. Pregnant women exposed to teratogens are counseled about increased risks and referred for detailed ultrasound evaluation to detect malformations.

Common infections that may be teratogenic include

Commonly used drugs that may be teratogenic include

Hyperthermia or exposure to temperatures > 39° C (eg, in a sauna) during the 1st trimester has been associated with spina bifida.

Exposure to Mercury

Mercury in seafood can be toxic to the fetus. The FDA (see Advice About Eating Fish: For Women Who Are or Might Become Pregnant, Breastfeeding Mothers, and Young Children) recommends the following:

  • Avoiding tilefish from the Gulf of Mexico, shark, swordfish, big-eye tuna, marlin, orange roughy, and king mackerel

  • Limiting albacore tuna to 4 ounces (one average meal)/week

  • Before eating fish caught in local lakes, rivers, and coastal areas, checking local advisories about the safety of such fish and, if levels of mercury are not known to be low, limiting consumption to 4 ounces/week while avoiding other seafood that week

Experts recommend that women who are pregnant or breastfeeding eat 8 to 12 ounces (2 or 3 average meals)/week of a variety of seafood that is lower in mercury. Such seafood includes flounder, shrimp, canned light tuna, salmon, pollock, tilapia, cod, and catfish. Fish has nutrients that are important for fetal growth and development.

Prior Stillbirth

Stillbirth Stillbirth Stillbirth is delivery of a dead fetus at > 20 weeks gestation. Maternal and fetal testing is done to determine the cause. Management is as for routine care after live delivery. Stillbirth,... read more is delivery of a dead fetus at > 20 weeks gestation. Fetal death during late pregnancy may have maternal, placental, or fetal anatomic or genetic causes (see table Common Causes of Stillbirth Common Causes of Stillbirth Stillbirth is delivery of a dead fetus at > 20 weeks gestation. Maternal and fetal testing is done to determine the cause. Management is as for routine care after live delivery. Stillbirth,... read more ). Having had a stillbirth or late abortion (ie, at 16 to 20 weeks) increases risk of fetal death in subsequent pregnancies. Degree of risk varies depending on the cause of a previous stillbirth. Fetal surveillance using antepartum testing (eg, nonstress testing, biophysical profile) is recommended.

Treatment of maternal disorders (eg, chronic hypertension, diabetes, infections) may lower risk of stillbirth in a current pregnancy.

Prior Preterm Delivery

Preterm delivery Preterm Labor Labor (contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities, infection... read more is delivery before 37 weeks. Previous preterm delivery due to preterm labor increases risk of future preterm deliveries; if the previous preterm neonate weighed < 1.5 kg, risk of preterm delivery in the next pregnancy is 50%.

Women with prior preterm delivery due to preterm labor should be closely monitored at 2-week intervals after 20 weeks. Monitoring includes

  • Ultrasound evaluation, including measurement of cervical length and shape, at 16 to 18 weeks

  • Uterine contraction monitoring

  • Testing for bacterial vaginosis

  • Measurement of fetal fibronectin

Women with a prior preterm birth due to preterm labor or with shortening (< 25 mm) or funneling of the cervix should be given 17 alpha-hydroxyprogesterone 250 mg IM once a week.

Prior Neonate With a Genetic or Congenital Disorder

Risk of having a fetus with a chromosomal disorder Risk Factors for Congenital Disorders Prenatal genetic counseling is provided for all prospective parents, ideally before conception, to assess risk factors for congenital disorders. Certain precautions to help prevent birth defects... read more is increased for most couples who have had a fetus or neonate with a chromosomal disorder (recognized or missed). Recurrence risk for most genetic disorders is unknown. Most congenital malformations are multifactorial; risk of having a subsequent fetus with malformations is 1%.

If couples have had a neonate with a genetic or chromosomal disorder, genetic screening Genetic Evaluation Genetic evaluation is part of routine prenatal care and is ideally done before conception. The extent of genetic evaluation a woman chooses is related to how the woman weighs factors such as... read more Genetic Evaluation is recommended. If couples have had a neonate with a congenital malformation, genetic screening, high-resolution ultrasonography, and evaluation by a maternal-fetal medicine specialist is recommended.

Polyhydramnios (Hydramnios) and Oligohydramnios

  • Uncontrolled maternal diabetes

  • Multifetal pregnancy

  • Isoimmunization

  • Fetal malformations (eg, esophageal atresia, anencephaly, spina bifida)

Oligohydramnios Oligohydramnios Oligohydramnios is a deficient volume of amniotic fluid; it is associated with maternal and fetal complications. Diagnosis is by ultrasonographic measurement of amniotic fluid volume. Management... read more (deficient amniotic fluid) often accompanies congenital malformations of the fetal urinary tract and severe fetal growth restriction (< 3rd percentile). Also, Potter syndrome with pulmonary hypoplasia or fetal surface compression abnormalities may result, usually in the 2nd trimester, and cause fetal death.

Polyhydramnios or oligohydramnios is suspected if uterine size does not correspond to gestational date or may be discovered incidentally via ultrasonography, which is diagnostic.

Multifetal (Multiple) Pregnancy

Prior Birth Injury

Most cerebral palsy Cerebral Palsy (CP) Syndromes Cerebral palsy refers to nonprogressive syndromes characterized by impaired voluntary movement or posture and resulting from prenatal developmental malformations or perinatal or postnatal central... read more and neurodevelopmental disorders are caused by factors unrelated to a birth injury. Injuries such as brachial plexus damage can result from procedures such as forceps or vacuum extractor delivery but often result from intrauterine forces during labor or malposition during the last weeks of pregnancy.

Previous shoulder dystocia Shoulder dystocia Fetal dystocia is abnormal fetal size or position resulting in difficult delivery. Diagnosis is by examination, ultrasonography, or response to augmentation of labor. Treatment is with physical... read more is a risk factor for future dystocia, and the delivery records should be reviewed for potentially modifiable risk factors (eg, fetal macrosomia, operative vaginal delivery) that may have predisposed to the injury.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Test your knowledge

Menopause
Which of the following is the most effective treatment for relieving symptoms associated with menopause? 
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
TOP