20 weeks pregnant
At 20 weeks you are halfway, in the second trimester, and your baby measures about 25 cm from head to heel and weighs about 300 g, roughly the length of a large banana. This is the week of the morphology scan in most Australian hospitals, and the whooping cough vaccine window opens.
Weighs about 300 g, like a large orange. Averages from standard growth tables; your scan gives your baby's own numbers.
Your baby at 20 weeks
Halfway. The baby swallows amniotic fluid and meconium forms in the gut. The body is catching up with the head, the face looks human and movements are becoming coordinated.
How you might feel
Round-ligament pains and backache are common as the bump shows, and sleeping on your side is recommended from now. Energy is usually good in these middle weeks.
Morphology scan. The whooping cough vaccine window opens (20–32 weeks).
Call the maternity unit today for bleeding, fluid loss, a severe headache or vision changes. 13 HEALTH (13 43 25 84) in Queensland; 000 in an emergency.
What's due this week in Australia
Tell your employer (when you are ready)
There is no legal deadline to tell your employer, but protections start once they know: transfer to a safe job, no-safe-job leave and special maternity leave.
Morphology (anatomy) ultrasound
A detailed 30–60 minute scan of the baby’s organs, spine, heart and limbs, the placenta position and the cervix.
Whooping cough (pertussis) vaccine
Free under the National Immunisation Program in every pregnancy.
20-week antenatal visit
Review of the morphology scan, blood pressure, the first fundal-height measurement and a chat about the baby’s movements.
Book antenatal classes and a hospital tour
Public hospitals run free or low-cost childbirth, breastfeeding and early-parenting classes, in person or online.
Put your name on childcare waitlists
If you plan to use childcare in the first year, many centres have waitlists of 6–12 months.
Coming up: 24–25-week antenatal visit (first pregnancy)
Blood pressure, fundal height, the baby’s movements, and the request forms for the glucose test and 28-week bloods.
Coming up: Gestational diabetes test (OGTT)
A fasting 75 g oral glucose tolerance test at a pathology collection centre: a fasting blood sample, the drink, then samples at 1 and 2 hours.
Checklist for the week
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Questions about 20 weeks
How many months is 20 weeks pregnant?
About four and a half months and the halfway point of a 40-week pregnancy. Hospitals count in weeks.
What trimester is 20 weeks?
Week 20 is in the second trimester. In the Australian guidelines Hello Bub follows, the first trimester runs to 13 weeks, the second from 14 to 27 and the third from 28 weeks.
What is checked at the 20-week scan?
The brain, face, spine, heart, kidneys, stomach, limbs, placenta position and the amount of fluid; it is the main anatomy check of the pregnancy.
Written by the Hello Bub team; medical schedule follows the Australian Pregnancy Care Guidelines; last reviewed 3 November 2026.