Pregnancy — Stages, Prenatal Care, Complications & Delivery Guide — Symptoms, Causes & Treatment | MyMedicPlus

Pregnancy (gestation) is the period of development from fertilisation of an ovum through implantation in the uterus to birth, spanning approximately 40 weeks (280 days) from the first day of the last menstrual period (LMP). It is divided into three trimesters: first trimester (weeks 1-12) — rapid embryonic development, organogenesis, and highest risk of miscarriage; second trimester (weeks 13-26) — foetal growth and maturation, typically the most comfortable trimester; and third trimester (weeks 27-40) — continued foetal growth, preparation for delivery, and most common period for late-pregnancy complications. Normal term delivery is between 37-42 weeks; pre-term birth (below 37 weeks) occurs in approximately 10% of pregnancies globally and is the leading cause of neonatal morbidity and mortality. The expected date of delivery (EDD) is calculated as LMP + 280 days (Naegele's rule) and confirmed by first-trimester ultrasound (dating scan at 11-14 weeks — most accurate dating tool). Approximately 140 million births occur annually worldwide. Globally, approximately 1 in 6 pregnancies is affected by a complication requiring specialist care — from gestational diabetes to pre-eclampsia and preterm labour.

Pregnancy begins with fertilisation — the union of a spermatozoon and secondary oocyte, typically in the ampulla of the fallopian tube, forming a zygote. The zygote undergoes rapid cell division (cleavage) as it travels toward the uterus over 5-6 days, forming a morula then a blastocyst. Implantation occurs approximately 6-10 days after fertilisation — the blastocyst invades the uterine endometrium (made receptive by progesterone from the corpus luteum). Human chorionic gonadotrophin (hCG — the basis of pregnancy tests) is secreted by trophoblast cells from implantation, rising rapidly in early pregnancy (doubling every 48-72 hours) and maintaining corpus luteum progesterone production until the placenta takes over at 8-10 weeks. Progesterone (from corpus luteum then placenta) maintains uterine quiescence and inhibits menstruation. The placenta — the functional organ of pregnancy — is fully established by 12 weeks, providing oxygen, nutrients, and hormones while removing foetal waste. Risk factors for pregnancy complications: advanced maternal age (above 35), obesity (BMI above 30), pre-existing conditions (diabetes, hypertension, kidney disease, autoimmune disorders), multiple pregnancy (twins or higher-order), prior pregnancy complications, and smoking or substance use.

Early pregnancy signs (first trimester): missed period (most sensitive early symptom); positive home pregnancy test (urine hCG detectable from approximately day 10-14 post-fertilisation — most reliable from the day of missed period); nausea and vomiting (affect 70-80% of pregnant women — typically from 6-12 weeks, resolving by 16-20 weeks in most; hyperemesis gravidarum — severe vomiting with more than 5% weight loss and ketonaemia — occurs in 1-2% and requires hospital treatment); breast tenderness and enlargement; urinary frequency (uterus pressing on bladder, increased GFR); fatigue; food aversions or cravings; and implantation bleeding (light spotting around 10-14 days post-conception — can be confused with a very light period). Second trimester: foetal movements ('quickening' — typically felt by the mother from 16-20 weeks in multigravida, 18-22 weeks in primigravida); round ligament pain; backache; and heartburn (from lower oesophageal sphincter relaxation from progesterone). Third trimester: breathlessness (diaphragm elevation from uterine size); oedema of ankles and feet; Braxton Hicks contractions (irregular, painless practice contractions); urinary urgency; insomnia; and pelvic girdle pain. Warning symptoms at any stage requiring urgent evaluation: heavy vaginal bleeding; severe abdominal pain; sudden severe headache; visual disturbance; facial swelling (possible pre-eclampsia); reduced foetal movement; and signs of preterm labour.

Pregnancy confirmation: urine human chorionic gonadotrophin (hCG) test — home pregnancy tests are over 99% accurate from the day of missed period. Serum hCG: quantitative, useful for monitoring early pregnancy viability (doubling time) and ectopic pregnancy. Dating and viability ultrasound (8-12 weeks): confirms intrauterine pregnancy, number of foetuses, establishes gestational age (crown-rump length measurement), and assesses cardiac activity. First-trimester screening (11-13+6 weeks): combined test (nuchal translucency ultrasound + serum free beta-hCG and PAPP-A) screens for Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13) — detection rate approximately 90% for Down syndrome. Cell-free DNA (cfDNA) testing (NIPT — non-invasive prenatal testing) from 10 weeks: screens for major trisomies with greater than 99% sensitivity for trisomy 21. Diagnostic testing (when indicated): chorionic villus sampling (CVS — 11-13 weeks) or amniocentesis (from 15 weeks) for definitive chromosomal diagnosis. Anatomy scan (anomaly scan — 18-22 weeks): detailed assessment of foetal anatomy — detects structural abnormalities. Glucose challenge test (24-28 weeks): screens for gestational diabetes. Serial growth scans in high-risk pregnancies from 28-32 weeks. Group B Streptococcus (GBS) swab at 35-37 weeks (UK: risk-based approach; USA: universal screening).

Preconception care: folic acid 400 mcg/day (5 mg for high-risk women — diabetes, epilepsy, prior NTD-affected pregnancy) started at least 1 month before conception and continued for the first 12 weeks reduces neural tube defect (spina bifida, anencephaly) risk by 70%. Vitamin D supplementation 10 mcg/day throughout pregnancy and breastfeeding. Antenatal appointments (NICE schedule for low-risk nulliparous women: 10 appointments): booking appointment at 8-10 weeks (history, blood tests — FBC, blood group, rubella immunity, HIV, syphilis, hepatitis B, haemoglobinopathy screening), followed by scheduled visits including anatomy scan, glucose tolerance testing, and foetal wellbeing assessments. Major pregnancy complications and management: Gestational diabetes mellitus (GDM): dietary modification and blood glucose monitoring; metformin if targets not met; insulin if metformin insufficient; birth by 40+6 weeks. Pre-eclampsia (characterised by new hypertension with proteinuria or end-organ dysfunction after 20 weeks): aspirin 75-150 mg from 12 weeks for high-risk women (reduces pre-eclampsia risk by 20-25%); anti-hypertensives (labetalol, nifedipine) for systolic above 160 mmHg; delivery if severe or not controlled. Preterm labour (PTL, below 37 weeks): antenatal corticosteroids (betamethasone or dexamethasone) for foetal lung maturation (most critical intervention — reduces neonatal respiratory distress syndrome by 40%); tocolytics (nifedipine, atosiban) for short-term delay of delivery to complete steroid course; magnesium sulfate for neuroprotection (reduces cerebral palsy) in imminent preterm birth below 32 weeks. Normal labour is managed across three stages: first stage (cervical dilatation from 0 to 10 cm); second stage (active pushing and delivery of baby); third stage (delivery of placenta).

Pregnancy is associated with a broad spectrum of potential complications across all trimesters and the postpartum period. First trimester: miscarriage affects approximately 10–20% of clinically recognised pregnancies, most commonly due to chromosomal abnormalities; hyperemesis gravidarum (severe nausea and vomiting causing dehydration and hospitalisation) affects 0.5–2%; ectopic pregnancy affects 1–2% and is a life-threatening emergency if not identified early. Second and third trimester: pre-eclampsia complicates 2–8% of pregnancies — severe forms cause seizures (eclampsia), HELLP syndrome, and maternal or perinatal death; gestational diabetes affects 6–9% of UK pregnancies and increases macrosomia, caesarean delivery, and maternal risk of type 2 diabetes; placental abruption (premature separation) causes haemorrhage, fetal distress, and preterm birth; placenta praevia (low-lying placenta covering the cervical os) requires planned caesarean delivery. Fetal and neonatal complications: intrauterine growth restriction (IUGR) increases risk of stillbirth, neonatal hypoglycaemia, and hypoxia; preterm birth (below 37 weeks) is the leading cause of perinatal mortality and morbidity — prematurity causes neurodisability, respiratory distress syndrome, necrotising enterocolitis, and sepsis; stillbirth affects approximately 1 in 200 pregnancies in the UK and rates are higher in obesity, advanced maternal age, and reduced fetal movements. Postpartum complications: postpartum haemorrhage (PPH — blood loss above 500 mL after vaginal delivery) is the leading cause of maternal mortality globally; postpartum depression affects 10–15% of mothers; venous thromboembolism is significantly elevated in the postpartum period, particularly following caesarean section.

Preconception optimisation: achieve healthy weight (BMI 18.5-24.9 — obesity increases risk of GDM, pre-eclampsia, miscarriage, and congenital abnormalities); start folic acid; review all medications with a doctor (some are teratogenic — ACE inhibitors, valproate, retinoids, warfarin, methotrexate); optimise control of chronic conditions (diabetes, epilepsy, thyroid disease); achieve rubella immunity (vaccination before pregnancy); and stop smoking, alcohol, and recreational drugs (no safe level of alcohol in pregnancy). During pregnancy: avoid listeria-risk foods (unpasteurised dairy, soft cheeses, pâté, undercooked meat and poultry — listeria causes miscarriage, preterm birth, and neonatal sepsis); avoid mercury-rich fish (shark, swordfish, marlin — limit tuna to 2 portions per week); food safety (wash salad, cook eggs thoroughly, avoid liver in first trimester — high vitamin A); no alcohol (fetal alcohol spectrum disorder); maintain physical activity (150 minutes moderate intensity per week — reduces GDM, pre-eclampsia, and promotes healthy birth weight); attend all antenatal appointments; and seek prompt medical attention for any warning symptoms.

Seek emergency care immediately (999/911 or maternity assessment unit) for: heavy vaginal bleeding at any stage of pregnancy (possible miscarriage, placenta praevia, placental abruption, or vasa praevia); severe abdominal pain, especially one-sided in early pregnancy (possible ectopic pregnancy — a life-threatening emergency); sudden severe headache with visual disturbance, facial swelling, or upper abdominal pain in the second or third trimester (possible pre-eclampsia); significantly reduced foetal movements after 28 weeks (foetal kick count below 10 in 2 hours — contact maternity triage); signs of preterm labour (regular painful contractions, rupture of membranes, or unusual vaginal discharge before 37 weeks); and high fever above 38°C with rigors or signs of urinary infection (increased risk of preterm labour). Attend routine appointments as scheduled — antenatal care is evidence-based and each appointment serves a specific screening and monitoring purpose.