Week 20 is the halfway mark. The anomaly scan often falls here, and in the UK it is usually the week whooping cough vaccination is offered. It is also the week the measuring changes, which is worth knowing before the numbers jump.
Your body this week
Leg cramps become a feature for many women around now — sharp pains in the calf that wake you at night. The NHS advice is to rub the muscle hard or pull the toes up towards the ankle, and notes that more daytime exercise may reduce how often they happen.
In the UK, a Maternity Certificate (MAT B1) is issued from 20 weeks onwards and is what maternity pay and benefits are claimed with. Ask your midwife or doctor for it rather than waiting to be offered it.
What you may notice
Tiredness and sleep problems, stretch marks, sore gums, round ligament pains, headaches, nosebleeds, bloating and constipation, indigestion and heartburn, sore breasts, leg cramps, feeling hot, dizziness, swollen hands and feet, urine infections, vaginal infections, and skin and hair changes.
Movements have started for many women by now and are still irregular. Nothing yet is a pattern, and nothing yet is worth counting.
Your baby this week
Around week 20, the NHS gives a figure of about 25.6cm and compares it to a banana. That number looks like a sudden jump, and it is: from this week measurements are taken head to heel rather than head to bottom, because before now the legs are curled up and hard to see. Population averages, as always, rather than a measurement of any one pregnancy.
A greasy white layer called vernix now covers the skin, thought to stop it drying out in the amniotic fluid and to help with the journey through the birth canal. Activity increases week by week — kicking, turning and thumb-sucking, which develops the reflex needed for feeding.
What care usually happens around now
The anomaly scan is offered between 18 and 20 weeks in England.
The whooping cough vaccination is recommended for every pregnant woman in the UK and is usually offered around week 20, with a window from week 16 to week 32. The point of the timing is that immunity crosses the placenta and protects a baby in the weeks before their own first vaccinations at eight weeks old. CDC recommends maternal vaccination in pregnancy for the same reason, on a US schedule. Which vaccines are offered, and when, differs between countries — ask what applies where you are.
This week's tip
Ask for your MAT B1 form at your next appointment, or the equivalent where you live. Maternity pay claims have deadlines, employers need the certificate rather than your word, and it is the paperwork most often remembered at week 32 in a panic.
When to see a doctor
Report bleeding, severe pain, a fever, or a headache with vision changes. Sudden swelling of the face or hands needs care today. Pregnancy warning signs has the full list.
Seek care now: Contact your local emergency services or go to your nearest emergency department if you have heavy bleeding, severe or one-sided tummy pain, a severe headache with vision changes, sudden swelling of the face or hands, a fever, fluid leaking from the vagina, chest pain, trouble breathing, fainting, or a seizure. Femio cannot assess a pregnancy.
Frequently asked questions
Why did the length jump so much this week?
Because the measurement changed from head-to-bottom to head-to-heel. Nothing grew that fast.
Is the whooping cough vaccination safe in pregnancy?
It is recommended in pregnancy by the NHS and by other national programmes, and the timing exists so that protection reaches a baby before their own vaccinations start. Week 21 covers catching up if you missed it, and week 19 covers the week before.