Overview of pregnancy complications

Last reviewed: 2 Jan 2023
Last updated: 10 Jan 2023

This page compiles our content related to pregnancy complications. For further information on diagnosis and treatment, follow the links below to our full BMJ Best Practice topics on the relevant conditions and symptoms.



Antenatal care is a key component of a healthy pregnancy. Regular antenatal care helps to identify and treat complications and to promote healthy behaviours.

Nausea and vomiting in pregnancy (NVP), commonly referred to as morning sickness, typically begins between the fourth and eighth week after the last menstrual period. It is characterised by nausea and vomiting that occurs more frequently during the morning hours, and typically resolves in the second trimester. NVP affects most pregnant women. Hyperemesis gravidarum is the most severe form of NVP and is characterised by persistent vomiting, volume depletion, ketosis, electrolyte disturbances, and weight loss.

Pregnant and lactating women have an increased folate demand, which can result in folate deficiency. Folate deficiency during pregnancy is strongly associated with fetal neural tube defects, 70% of which can be prevented by increased folic acid supplementation.[1][2][3]

In pregnant women, iron deficiency anaemia is defined as haemoglobin <11 g/dL (110 g/L ).[4] Symptoms include fatigue, low energy levels, and dyspnoea on exertion. Pregnancy increases demand for iron with a net loss of approximately 580 mg of iron during the gestation period, with the highest loss occurring in the third trimester.[5][6] Iron deficiency during the first 2 trimesters is associated with an increase in pre-term delivery and low birth-weight babies.[7]

Defined as an involuntary, spontaneous loss of a pregnancy before 20-24 completed weeks (gestation varies, depending on country).[8] It is associated with unprovoked vaginal bleeding with or without supra-pubic pain. Miscarriage occurs in up to one third of pregnancies.[9][10][11][12][13] Serial serum beta hCG titres and a transvaginal ultrasound scan aid in diagnosis.

More than half of women with recurrent miscarriage have unexplained or idiopathic recurrent miscarriage, where no cause or association can be identified.[14][15] Increasing maternal age and number of previous miscarriages increase the risk of further miscarriages. Definite associations of recurrent miscarriage include chromosomal abnormalities, antiphospholipid syndrome, certain structural uterine abnormalities such as cervical incompetence, and certain thrombophilias.

Defined as a fertilised ovum implanting and maturing outside of the uterine endometrial cavity, with the most common site being the fallopian tube (97%), followed by the ovary (3.2%) and the abdomen (1.3%).[16] Classic symptoms and signs are pain, vaginal bleeding, and amenorrhoea.[17] Red flags suggesting possible rupture include unstable vital signs (orthostatic changes), blood in the vaginal vault, or signs of intra-peritoneal bleeding (e.g., acute abdomen, shoulder pain, cervical motion tenderness). Risk increases with prior ectopic pregnancy, tubal surgery, history of sexually transmitted infections, smoking, in vitro fertilisation, or if pregnant despite IUD usage.

Defined as the placenta overlying the cervical os. Can be complete, partial, marginal, or low lying. Partial, marginal, and low-lying placenta praevia may resolve as pregnancy progresses. Symptomatic placenta praevia typically presents as second or third trimester painless vaginal bleeding.[18][19][20] Risk factors include uterine scarring (most commonly due to prior caesarean section), advanced maternal age, smoking, previous multiple pregnancies/short inter-pregnancy intervals or miscarriages/induced abortions, prior placenta praevia, infertility treatment, and illicit drug use. 

Hydatidiform moles are chromosomally abnormal pregnancies that have the potential to become malignant (gestational trophoblastic neoplasia). Gestational trophoblastic disease (GTD) includes tumours of fetal tissues, including hydatidiform moles, arising from placental trophoblasts. The most common presenting symptom is vaginal bleeding and patients typically present in the first trimester. Women are commonly at the extremes of reproductive life (younger than 20 years of age or over 35 years of age), and may relate a history of prior GTD.[21][22]

Early pregnancy causes of abdominal pain include ectopic pregnancy, miscarriage and ovarian hyper-stimulation syndrome. Late pregnancy causes include pre-term labour, chorioamnionitis, uterine rupture, placental abruption, HELLP syndrome, and acute fatty liver of pregnancy. Gynaecological causes include adnexal masses and fibroids. Other aetiologies can be urological (e.g., UTIs, acute pyelonephritis, nephrolithiasis, and hydro-nephrosis), gastrointestinal (e.g., appendicitis, cholecystitis, pancreatitis, and intestinal obstruction), trauma-related, and musculoskeletal.

Defined by a blood pressure ≥140/90 mmHg on two occasions (at least 4 hours apart) during pregnancy after 20 weeks gestation in a previously normotensive woman, without the presence of proteinuria (<300 mg/24 hours) or other clinical features suggestive of pre-eclampsia (thrombocytopenia, impaired renal or kidney function, pulmonary oedema, or new-onset headache). The pregnant woman is usually asymptomatic. Risk factors include nulligravidy, black or Hispanic ethnicity and mothers who were born small for their gestational age.[23][24][25][26][27][28] Gestational hypertension increases the risk of macrosomia, caesarean delivery, and admission of the neonate to the intensive care unit. Co-existence of gestational diabetes further increases the risk.[29]

Develops during pregnancy and is usually recognised by screening at 24 to 28 weeks of gestation on the basis of elevated plasma glucose levels on glucose tolerance testing. Risk factors include advanced maternal age (>40 years), elevated BMI, polycystic ovarian syndrome, non-white ancestry, family history of type 2 diabetes, lack of exercise, and prior gestational diabetes.[30][31][32][33][34][35][36][37][38] Sequelae include fetal macrosomia, caesarean section, birth injuries, and neonatal hypoglycaemia or polycythaemia.

Pregnancy can also be complicated by established type 1 or type 2 diabetes.

An infection of the kidneys, bladder, or urethra. Urinary tract infections (UTIs) in pregnancy are considered to be complicated UTIs. Pregnant women should be screened for asymptomatic bacteriuria as it has been associated with higher rates of pyelonephritis and premature labour.[39][40] 

Bacterial vaginosis continues to be a leading cause of vaginitis; other common infectious causes include trichomoniasis and candidiasis, although non-infectious causes are also possible. Common symptoms include discharge, pruritus, and dyspareunia. Bacterial vaginosis and trichomoniasis have been associated with pre-term delivery, low birth weight, and premature rupture of membranes.

A food-borne infection caused by a motile, non-spore-forming, Gram-positive bacillus. Pregnant women are advised to avoid raw unwashed vegetables, raw or undercooked meat (poultry, beef, pork), leftover food, soft cheeses, and unpasteurised milk or its products. Pregnant women may have flu-like symptoms (lethargy, fever, arthralgias, myalgias, rigors, fatigue, diarrhoea, vomiting, and abdominal pain).[41]

Parasitic disease caused by the protozoan Toxoplasma gondii. Spreads through food or water contaminated with oocysts, infected meat, or contact with oocysts from feline faeces. Transplacental transmission results only when a seronegative woman acquires toxoplasmosis during pregnancy. Primary infection during pregnancy is often asymptomatic in the mother, but can result in fetal death and severe congenital abnormalities (e.g., intellectual disability and blindness). Fetal infections in the third trimester are often asymptomatic at birth, but can lead to problems months to years later.[42] Routine antenatal screening for Toxoplasma is recommended in some countries (e.g., France).

Cytomegalovirus (CMV) is a ubiquitous beta-herpes virus that infects the majority of humans and establishes a state of lifelong latency in host cells. Periodic sub-clinical re-activations are controlled by a functioning immune system. The immunologically-naive fetus is at risk of congenital CMV disease and its complications, such as hearing loss and neurological deficits. Pregnant mothers should wash their hands regularly and thoroughly to prevent primary infection (which is usually asymptomatic).

Maternal infection in pregnancy, particularly early in gestation, that may cause spontaneous abortion, fetal death, or a wide spectrum of anatomical and laboratory anomalies (congenital rubella syndrome). Specialty consultation is strongly recommended for pregnant women with exposure to rubella.

Characteristic clinical findings include fever, an itchy maculopapular (sometimes morbilliform) rash, arthralgia, and non-purulent conjunctivitis.[43] No differences in clinical presentation have been described between pregnant women and non-pregnant patients.

Congenital Zika syndrome is a pattern of congenital anomalies (i.e., microcephaly, intracranial calcifications or other brain anomalies, or eye anomalies, among others) in infants associated with Zika virus infection during pregnancy.[44][45][46][47]

It is recommended that all pregnant women be tested for HIV infection as early as possible in pregnancy.[48] All pregnant women with HIV should receive antiretroviral therapy (ART), as early as possible in the pregnancy, regardless of CD4 count or viral load.

Group B streptococci, also known as Streptococcus agalactiae, are Gram-positive bacteria that normally colonise the Gl tract, perineum, and vagina. They can cause invasive infections at any age but infections are most common in the neonatal period, in older people, and in adults with predisposing factors (i.e., pregnancy, diabetes, immunocompromised). 

Intrahepatic cholestasis of pregnancy (ICP) is a disorder characterised by maternal pruritus (itch) and liver dysfunction, in the absence of other contributing liver disorders and restricted to pregnancy. Risk factors include previous or family history of ICP, cholelithiasis, and history of hepatitis C.[49][50][51][52] Maternal complications include an increased risk of gestational diabetes and pre-eclampsia, in addition to impaired glucose tolerance and dyslipidaemia; fetal complications include pre-term birth, meconium-staining of the amniotic fluid, neonatal unit admission, and, in pregnant women with bile acid concentrations of ≥100 micromol/L, intra-uterine fetal death (stillbirth).[53]

A disorder of pregnancy associated with new-onset hypertension (defined as a systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg), which occurs most often after 20 weeks of gestation and frequently near term. Although often accompanied by new-onset proteinuria, hypertension and other signs or symptoms of pre-eclampsia may present in some women in the absence of proteinuria.[54] The woman may be asymptomatic and diagnosed at a routine clinic visit, or she may present acutely with headache, upper abdominal pain, visual disturbances, breathlessness, seizures, and oliguria.

A severe form of pre-eclampsia characterised by haemolysis (H), elevated liver enzymes (EL), and low platelets (LP) in a pregnant or puerperal woman (usually within 7 days of delivery). The diagnosis of HELLP syndrome should be considered in any pregnant woman presenting in the second half of gestation or immediately post-partum with significant new-onset epigastric/right upper quadrant pain until proven otherwise. Associated with progressive and sometimes rapid maternal and fetal deterioration.

Separation of the normally located placenta before delivery of the fetus. May be concealed or overt.[55] Associated with increased peri-natal mortality and morbidity. Also a cause of significant maternal morbidity. Risk factors include smoking, trauma, hypertensive disorders, and cocaine use.

Pre-term birth occurs between 24 and 37 weeks' gestation. In two-thirds of cases, it occurs following spontaneous onset of labour. Only a minority of women who present with pre-term contractions known as threatened pre-term labour (TPTL) progress to actual labour and delivery. The remainder of pre-term birth is due to iatrogenic delivery, most commonly because of pre-eclampsia and intrauterine growth restriction.

Breech presentation in pregnancy occurs when a baby presents with the buttocks or feet rather than the head first (cephalic presentation) and is associated with increased morbidity and mortality for both the mother and the baby. It is common in early pregnancy and decreases with advancing gestational age, as most babies turn spontaneously to a cephalic presentation before birth.[56][57]

Rhesus (Rh) incompatibility is a condition where a Rh-negative mother carrying a Rh-positive fetus can produce antibodies against paternally-derived Rh antigens on fetal red blood cells. These antibodies can cross the placenta, and destroy fetal red blood cells. It is a leading cause of haemolytic disease of the fetus and newborn, also known as erythroblastosis fetalis.

In addition to immediate post-birth resuscitation, efforts to reduce excessive oxygen exposure, hyperventilation, hypothermia, and hypoglycaemia must be made.[58] Consultation with a neonatologist as soon as possible is recommended to reduce potential morbidity.

The development of a depressive illness following childbirth may form part of a bipolar or, more usually, a unipolar illness.[59] Postnatal depression is not recognised by current classification systems as a condition in its own right, but the onset of a depressive episode within 4 weeks of childbirth can be recorded via the peripartum-onset specifier in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, text revision (DSM-5-TR).[60] There is evidence to suggest that the DSM-5-TR specifier is too narrow.[61] Hence, in common usage, depressive episodes occurring within 6 to 12 months of delivery may be considered to be postnatal depression. Strong risk factors include history of depression, recent stressful life events, poor social support, and sleep deprivation.



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