Complications in pregnancy can result from conditions that are specifically linked to the pregnant state as well as conditions that commonly arise or occur incidentally in women who are pregnant. Serious sequelae might include miscarriage, pre-term labour or premature rupture of membranes, premature birth, stillbirth, low birth weight, macrosomia, birth defects, and infant and maternal morbidity or death. Complications affecting mother and fetus may arise at any stage of pregnancy, during labour, or postpartum.
Regular antenatal care/screening is a key component of a healthy pregnancy.
Nausea and vomiting in pregnancy (NVP), commonly referred to as morning sickness, typically begins between the fourth and seventh 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 woman are at a higher risk because of increased need for folate. Complications include neural tube defects, spontaneous abortion, and placental abruption. 
In pregnant women, iron deficiency anaemia is defined as haemoglobin below 110 g/L (<11 g/dL).  Symptoms include fatigue, low energy levels, and dyspnoea on exertion. Pregnancy increases demand for iron with a net loss of 680 mg of iron in 9 months or approximately 2.5 mg per day. Iron deficiency during the first 2 trimesters is associated with an increase in pre-term delivery and low birth-weight babies. 
Defined as an involuntary, spontaneous loss of a pregnancy before 22 completed weeks.  It is associated with unprovoked vaginal bleeding with or without supra-pubic pain. Miscarriage occurs in up to one third of pregnancies.      Serial serum beta hCG titres and a transvaginal ultrasound scan aid in diagnosis.
More than half of patients with recurrent miscarriage have unexplained or idiopathic recurrent miscarriage, where no cause or association can be identified.   Increasing maternal age and number of previous miscarriages increase the risk of further miscarriages. Anti-phospholipid syndrome (APS) is one of the known causes of first- and second-trimester recurrent miscarriage. APS is defined as the presence of anticardiolipin antibodies or lupus anticoagulant antibodies, in association with any of the following: 3 or more consecutive fetal losses before week 10 of gestation; 1 or more unexplained intrauterine deaths beyond 10 weeks of gestation; or 1 or more premature births before 34 weeks due to severe pre-eclampsia or impaired fetal growth.  No separate risk factors for APS are known.
Defined as a fertilised ovum implanting and maturing outside of the uterine endometrial cavity (e.g., in the fallopian tube, ovary, or abdomen).  Classic symptoms are abdominal pain, amenorrhoea, and vaginal bleeding.  Red flags include unstable vital signs or signs of intraperitoneal bleeding (e.g., acute abdomen, shoulder pain, cervical motion tenderness); urgent surgical intervention may be required to avoid maternal death. Risk factors include progesterone-releasing IUDs,  tubal sterilisation surgery,  and previous ectopic pregnancy or genital infections.
Defined as the placenta overlying the cervical os. Can be complete, partial, or marginal, and may resolve as pregnancy progresses. Symptomatic placenta praevia typically presents as second or third trimester painless vaginal bleeding.   Possible risk factors include multiple previous pregnancies,   uterine scarring (e.g., due to prior caesarean section),  multiple miscarriages,   previous induced abortion,   placental abnormalities, short inter-pregnancy intervals,  and illicit drug use. Sequelae include intrauterine growth restriction and premature delivery.
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. There is a significantly higher chance of GTD among women over 35 years of age, which increases progressively as maternal age advances. 
Early pregnancy causes of abdominal pain include ectopic pregnancy, miscarriage, ovarian hyper-stimulation syndrome, and pre-term labour. Late pregnancy causes include 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 sustained BP ≥140/90 mmHg in a previously normotensive patient, without the presence of proteinuria (<300 mg/24 hours). It is usually asymptomatic and more often occurs in the second half of pregnancy. Risk factors include nulliparity,    black or Hispanic ethnicity,   and mothers who were born small for their gestational age.  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. 
It is usually recognised by screening at 24 to 28 weeks of gestation. Risk factors include advanced maternal age (>40 years),  polycystic ovarian syndrome,   non-white ancestry,    family history of type 2 diabetes,  low-fibre and high glycaemic-index diet,   weight gain as a young adult,  lack of exercise,   and prior gestational diabetes.  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.
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. Sequelae include pre-term delivery. 
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 Listeria monocytogenes . Pregnant women are advised to avoid raw, undercooked, or processed meat and vegetables, soft cheeses, and leftover food. Complications of infection in pregnancy are stillbirth, abortion, and premature labour. 
Parasitic disease caused by the protozoan Toxoplasma gondii . Risk factors for exposure include ingestion of undercooked or raw meat, or water or food contaminated with cat faeces. Transplacental transmission results only when a seronegative woman acquires toxoplasmosis during pregnancy. Acute infection is often asymptomatic,  but can result in fetal death and severe congenital abnormalities (e.g., mental retardation and blindness). Fetal infections in the third trimester are often asymptomatic at birth, but can lead to problems months to years later.  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, however, is at high risk of CMV disease (acquired through vertical transmission of CMV) and its complications (e.g., microcephaly, intra-cranial calcification, hepatosplenomegaly, neurological abnormality, hearing loss, and mental retardation    ). Pregnant mothers should wash their hands regularly and thoroughly to prevent primary infection (which is usually asymptomatic). CMV screening in pregnancy is not routinely performed, but may identify those suitable for antiviral treatment. 
Maternal infection during pregnancy may cause spontaneous abortion, fetal death, or congenital anomalies.
Characteristic clinical findings include fever, an itchy maculopapular (sometimes morbilliform) rash, arthralgia, and non-purulent conjunctivitis.  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.    
It is recommended that all pregnant women be tested for HIV infection as early as possible.  To prevent vertical viral transmission, highly active antiretroviral agent (HAART) therapy is initiated as soon as possible in the pregnancy, irrespective of CD4 count or viral load.
Group B streptococci are gram-positive bacteria that 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 the elderly, and in adults with predisposing factors (particularly pregnancy and diabetes).
Intra-hepatic cholestasis of pregnancy (ICP) is a pruritic condition caused by impaired bile flow allowing bile salts to be deposited in the skin and the placenta. Usually presents in the third trimester with pruritus, which is worse at night, starts on the soles of feet and hands, and spares the face. Some women may present with jaundice and significant liver dysfunction, coagulopathy from vitamin K deficiency (rarely), abnormal fetal heart rate, premature labour, or intrauterine fetal demise. Risk factors include previous or family history of ICP,   age over 35 years,  and history of hepatitis C.  ICP may be confused with plaques, urticaria, and papules of pregnancy (PUPPS). Sequelae include premature birth and respiratory distress syndrome in pre-term infants.
Pre-eclampsia is the occurrence of BP ≥140/90 mmHg in the third trimester, with proteinuria ≥300 mg/24 hours, developing at the same time or shortly thereafter. Eclampsia is the occurrence of seizures without any other cause in a patient with pre-eclampsia.  Pre-eclampsia is usually asymptomatic but may present with headache, seizure, blurred vision, and abdominal pain. Risk factors include nulliparity (or first pregnancy with new partner), family history of pre-eclampsia, body mass index >30, maternal age >35 years, and multiple (twin) pregnancy.    Sequelae include placental abruption requiring caesarean section delivery.
Haemolytic anaemia, elevated liver enzymes, and low platelet count. Considered to be a variant of severe pre-eclampsia. 
Premature separation of the placenta from the uterus may be caused by trauma, hypertension, or coagulopathy.  It is a common cause of bleeding in the third trimester.
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 reasons for early 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.
Mothers sensitised to Rh factor in their first pregnancy may have problems when pregnant with a second Rh-positive child. Symptoms in the infant can range from mild to life-threatening hyperbilirubinaemia.
In addition to immediate post-birth resuscitation, efforts to reduce excessive oxygen exposure, hyperventilation, hypothermia, and hypoglycaemia must be made.  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 unipolar or, less frequently, a bipolar illness. It 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 postpartum-onset specifier in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).  There is evidence to suggest that the DSM-5 specifier is too narrow.  Hence, in common usage, depressive episodes occurring within 6 months of delivery may be considered to be postnatal depression. The overall prevalence of clinically significant postnatal depressive symptoms is estimated to be 7% to 19%, although estimates vary.   Strong risk factors include history of depression, recent stressful life events, poor social support, and sleep deprivation.
BMJ Publishing Group
This overview has been compiled using the information in existing sub-topics.
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