Pregnancy is a journey of remarkable milestones — each week bringing new developments for your baby and new experiences for you. Understanding what to expect at each stage, and which tests are recommended when, helps you navigate pregnancy with confidence and ensures your baby gets the best possible start.
First Trimester (Weeks 1–12)
Key Milestones
- Week 4–5: Implantation complete; heart begins to beat
- Week 6–7: Brain, spinal cord, and major organs begin forming
- Week 8: All major organs present in rudimentary form; embryo becomes a fetus
- Week 10–12: Fingers and toes form; fetus begins to move (though not yet felt)
Key Tests in the First Trimester
- Confirmation of pregnancy and dating scan (6–8 weeks): Confirms intrauterine pregnancy and establishes gestational age
- Blood tests: Blood group and Rh factor, full blood count, rubella immunity, HIV, hepatitis B and C, syphilis, thyroid function
- NIPT (Non-Invasive Prenatal Testing, from 10 weeks): Screens for chromosomal conditions including Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13) from a maternal blood sample — no risk to the pregnancy
- First-trimester combined screening (11–14 weeks): Nuchal translucency ultrasound + blood tests (PAPP-A, free beta-hCG) to assess chromosomal risk
- Chorionic Villus Sampling (CVS, 10–13 weeks): Diagnostic test for chromosomal abnormalities; recommended when screening indicates elevated risk
Second Trimester (Weeks 13–26)
Key Milestones
- Week 16–18: Baby's movements felt for the first time (quickening)
- Week 20: Anatomy scan; baby's sex can often be determined
- Week 24: Viability threshold — baby has a chance of survival if born prematurely
Key Tests in the Second Trimester
- Anatomy scan / anomaly scan (18–20 weeks): Detailed ultrasound assessing fetal anatomy, placental position, and amniotic fluid
- Quad screen (15–20 weeks): Blood test measuring AFP, hCG, estriol, and inhibin A to assess risk for Down syndrome, Trisomy 18, and neural tube defects
- Amniocentesis (15–20 weeks): Diagnostic test for chromosomal abnormalities; recommended when screening indicates elevated risk
- Glucose challenge test (24–28 weeks): Screens for gestational diabetes
Third Trimester (Weeks 27–40+)
Key Milestones
- Week 28: Baby's eyes open; brain development accelerates
- Week 32–36: Baby moves into head-down position in preparation for birth
- Week 37+: Full term; baby is ready for birth
Key Tests in the Third Trimester
- Growth scans: Monitor fetal growth and wellbeing
- Group B Streptococcus (GBS) swab (35–37 weeks): Screens for GBS colonization that could affect the baby during delivery
- Non-stress test (NST): Monitors fetal heart rate in response to movement
- Biophysical profile: Combines NST with ultrasound assessment of fetal breathing, movement, tone, and amniotic fluid
FAQs
Is NIPT better than the first-trimester combined screen?
NIPT has higher sensitivity and specificity for the common trisomies than first-trimester combined screening. However, NIPT is a screening test — positive results require confirmation with diagnostic testing (amniocentesis or CVS). Many doctors recommend NIPT as the preferred first-line screening for chromosomal conditions.
Are all these tests mandatory?
No. All prenatal tests are optional. The decision to test is personal and should be made after discussion with your obstetrician and, ideally, a genetic counsellor who can help you understand the implications of both testing and not testing.
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