Normal Pregnancy

Pregnancy triggers coordinated physiological adaptation across nearly every organ system, driven predominantly by placental hormones (human chorionic gonadotropin, progesterone, estrogen, human placental lactogen).

Cardiac output rises by roughly 30 to 40%, mostly via increased stroke volume in the first half of pregnancy and increased heart rate later, while systemic vascular resistance falls, producing a physiological drop in blood pressure that nadirs around 20 to 24 weeks before returning toward pre-pregnancy levels by term.

Plasma volume expands by 40 to 50%, outpacing the roughly 20 to 30% rise in red cell mass, producing a physiological, dilutional fall in hemoglobin (see Anaemia in Pregnancy entry).

Renal plasma flow and GFR rise by approximately 50%, lowering baseline creatinine and urea.

Tidal volume increases and a mild compensated respiratory alkalosis is normal, reflecting progesterone driven increased respiratory drive.

Expected symptoms include nausea (particularly first trimester, peaking around 9 weeks), breast tenderness, fatigue, urinary frequency, and, from roughly 18 to 20 weeks in a first pregnancy (slightly earlier in subsequent pregnancies), maternal awareness of fetal movement ("quickening").

Braxton Hicks contractions, irregular, painless uterine tightening, are normal from the second trimester onward and are distinct from true labor.

Urine or serum beta-hCG confirms pregnancy; serum quantitative hCG in a viable early pregnancy roughly doubles every 48 to 72 hours up to about 6 weeks
Dating: last menstrual period gives an estimate, but first trimester ultrasound crown-rump length (ideally 8 to 14 weeks) is the most accurate dating method, accurate to within roughly 5 to 7 days; used to redate the pregnancy if it differs from LMP-based dating by more than about 5 to 7 days
Routine screening per most national programs: combined first trimester screening (nuchal translucency plus PAPP-A plus free beta-hCG) at 11 to 13+6 weeks for aneuploidy risk; detailed anomaly scan at 18 to 22 weeks; 75g OGTT at 24 to 28 weeks for at-risk women (see Gestational Diabetes entry); group B streptococcus screening at 36 to 37 weeks where universal culture-based screening is practiced

Folic acid 400 mcg (0.4 mg) PO od, ideally from preconception through 12 weeks, to reduce neural tube defect risk; 5 mg PO od in high risk women (previous NTD affected pregnancy, on antiepileptic medication, diabetes, BMI ≥30, sickle cell disease, or malabsorption)
Iron and folic acid supplementation per local protocol (see Anaemia in Pregnancy entry); calcium 1.5 to 2 g/day in populations with low dietary calcium intake, reduces pre-eclampsia risk
Aspirin 75 to 150 mg PO od from 12 weeks for women meeting high or moderate risk criteria for pre-eclampsia (see that entry)
Anti-D prophylaxis for Rh negative women: routine antenatal dose (commonly 300 mcg) around 28 weeks per local protocol, plus a dose within 72 hours of any potentially sensitizing event (bleeding, trauma, invasive procedure, delivery)
Vaccination: inactivated influenza vaccine any trimester; pertussis-containing (Tdap) vaccine typically 16 to 32 weeks to passively protect the neonate; live vaccines avoided
Lifestyle counseling: smoking and alcohol cessation, dietary listeria and toxoplasmosis precautions, safe exercise, and education on danger signs (bleeding, reduced fetal movements, severe headache, visual disturbance) warranting urgent review

Clinical toolsCalculators

BMI GCS EDD Parkland Formula

Corrected Sodium Corrected Calcium Anion Gap Creatinine Clearance Insulin Calculations qSOFA Wells PE Wells DVT CHA₂DS₂-VASc HAS-BLED CURB-65 Centor/McIsaac

Multiple Pregnancy

Pregnancy with two or more fetuses, classified by zygosity and chorionicity, the latter being the single most important determinant of risk and management pathway.

Dichorionic diamniotic (DCDA) twins (either dizygotic, or monozygotic splitting within 3 days of fertilization) have separate placentas and carry the lowest risk.

Monochorionic diamniotic (MCDA) twins (monozygotic splitting 4 to 8 days post-fertilization) share a single placenta with a shared circulation, carrying specific risks including twin-to-twin transfusion syndrome.

Monochorionic monoamniotic (MCMA) twins (splitting after day 8) share both placenta and amniotic sac, carrying the highest risk given the potential for cord entanglement.

Uterine size greater than expected for dates, exaggerated pregnancy symptoms (nausea, breathlessness), and, later in pregnancy, palpation of multiple fetal poles.

Multiple pregnancy carries substantially elevated risk of nearly every obstetric complication: hyperemesis, pre-eclampsia, gestational diabetes, anemia, preterm labor (the leading cause of perinatal morbidity in twins), malpresentation, and postpartum hemorrhage.

Chorionicity must be determined by ultrasound in the first trimester (ideally 11 to 14 weeks), since it becomes progressively harder to assess later and dictates the entire subsequent management pathway; the lambda sign (a triangular projection of placental tissue between the membranes at the base) indicates dichorionicity, while the T-sign (membranes meeting the placenta at a right angle) indicates monochorionicity
Serial growth scans are more frequent than in singleton pregnancy: every 4 weeks from 20 weeks in DCDA twins, every 2 weeks from 16 weeks in MCDA twins, given the need for early detection of twin-to-twin transfusion syndrome
Screening for twin-to-twin transfusion syndrome in monochorionic twins uses ultrasound assessment of amniotic fluid discordance (oligohydramnios in one sac, polyhydramnios in the other) and bladder visualization, staged using the Quintero staging system

Aspirin 75 to 150 mg PO od from 12 weeks, given multiple pregnancy is itself a risk factor for pre-eclampsia
Increased iron and folate supplementation given elevated anemia risk
Twin-to-twin transfusion syndrome (MCDA twins): significant or progressive disease (Quintero stage II or above) is treated with fetoscopic laser ablation of the shared placental vascular anastomoses at a specialist fetal medicine center, offering the best outcomes compared with amnioreduction alone
Timing of delivery: uncomplicated DCDA twins, offer delivery from 37 to 37+6 weeks; uncomplicated MCDA twins, offer delivery from 36 to 37 weeks (after a course of corticosteroids given the earlier timing); MCMA twins are typically delivered by planned cesarean around 32 to 34 weeks, given the ongoing cord entanglement risk, often with prior admission for continuous monitoring from around 26 to 28 weeks
Mode of delivery: vaginal delivery is generally appropriate if the first (presenting) twin is cephalic, with cesarean considered for a non-cephalic first twin, MCMA twins, or other specific complications; delivery of twins should occur in a unit with immediate access to cesarean facilities given the risk of complications with the second twin
Active management of the third stage is essential given substantially elevated postpartum hemorrhage risk from uterine overdistension, with oxytocin infusion often continued for a longer duration postpartum

Referral: obstetric-led care for all multiple pregnancies; specialist fetal medicine center for monochorionic twins and any suspected twin-to-twin transfusion syndrome.

Normal Pregnancy

Overview

Clinical Features

Diagnosis

Management

Overview

Clinical Features

Diagnosis

Management