Pregnancy ultrasound timeline: which scans you need, and when
The four standard pregnancy ultrasound scans, what each one looks for, when to have them, and how mobile sonography fits in for high-risk or remote-area mothers.
A standard, low-risk pregnancy in Kenya involves four ultrasound scans across the nine months. Knowing what each one is for — and when to schedule it — gives you peace of mind and helps your obstetrician catch issues early.
Scan 1 — dating scan (6 to 9 weeks)
Done transvaginally most of the time, the dating scan confirms the pregnancy is in the uterus (rules out ectopic), counts the number of embryos, confirms a heartbeat, and accurately dates the pregnancy from the embryo's crown-rump length. This is the most accurate date you'll get — more accurate than the last menstrual period.
Scan 2 — nuchal translucency / first-trimester scan (11 to 14 weeks)
This scan measures the fluid behind the baby's neck (the nuchal translucency) and combines it with a blood test to estimate risk for Down syndrome and other chromosomal conditions. It also confirms major structures are developing normally and refines the due date.
Scan 3 — anomaly / mid-trimester scan (18 to 22 weeks)
The most detailed scan of the pregnancy. The sonographer systematically checks the baby's brain, heart, spine, kidneys, abdominal wall, limbs, and placenta. This is when most structural anomalies are picked up. It's also when many parents choose to learn the sex.
Scan 4 — growth / well-being scan (32 to 36 weeks)
Measures the baby's size, position, and amniotic fluid level, and confirms the placenta isn't blocking the cervix. Critical for planning the birth — particularly whether vaginal delivery is safe or whether a caesarean section should be planned.
Optional 3D/4D bonding scans
Done around 26 to 32 weeks, 3D/4D scans aren't diagnostic — they're for the parents. The image quality depends heavily on the baby's position, the placenta's location, and the amount of amniotic fluid. A skilled sonographer with portable equipment can often get a great image in your living room.
When mobile sonography is the better option
- High-risk pregnancies on bed rest where hospital travel is medically discouraged.
- Patients in rural counties where the nearest sonography unit is more than two hours away.
- Twin or triplet pregnancies that need more frequent monitoring than a clinic schedule allows.
- Anxious first-time mothers who would benefit from being scanned in a calm, familiar environment.
Don't skip scan 3
The 20-week anomaly scan is the most clinically important of the four. If you only manage two scans in your entire pregnancy, make them the dating scan and the anomaly scan.