What is happening in week 4
Doctors count pregnancy weeks from the first day of your last period, so week 4 sits in the first trimester (up to the end of week 13). That is about 36 weeks to go until week 40, and about 0.9 months by a rough conversion. Around week 4 the embryo is about 2mm long and is growing fast inside its fluid-filled sac.
Your baby
The NHS guide describes the embryo at about 2mm long (the size of a poppy seed), sitting in an amniotic sac and attached to a yolk sac that feeds it. The outer layer will go on to form the placenta, which brings oxygen and nutrients.
Your body
You probably do not look pregnant yet, and many people have no symptoms. When the hormone hCG starts to rise you may notice a missed period, sore breasts, nausea, tiredness or a metallic taste. Home pregnancy tests can pick up a pregnancy from about 3 and a half weeks, according to the NHS.
This week’s to-do
- Confirm the pregnancy with a doctor and ask about starting antenatal care early.
- Ask your doctor about folic acid, which the NHS advises taking until at least week 12 to support the baby’s nervous system.
- Eat a varied, balanced diet; you do not need to eat for two. Avoid smoking and alcohol and cut back on caffeine.
When to call
Call your doctor or hospital if you have any bleeding, even light spotting, or if you feel very low or anxious.
Chaitanya Hospital in Kadapa, near RTC Bus Stand, Simhapuri Colony, provides delivery and emergency care 24/7. Our antenatal check-ups team can answer questions about your own pregnancy.
Use the week-by-week guide to jump to your week, or the due date calculator to work out your dates. Timings for scans and tests come from NHS guidance in the UK and can differ from your doctor’s schedule, so always follow your own doctor’s advice. This page is educational and not a substitute for a doctor.
Sources
Text on this page is paraphrased from the sources above. Sizes are averages and vary between babies.