You are 6 weeks exactly

By the end of week 6, one of your baby's major organs, the heart, is developing fast and circulating blood.

238 days until your due date

Your embryo may still be tiny, but it's going through rapid, complex development.

The heartbeat is now easier to see on an ultrasound scan. The heart starts as a simple smooth tube, which becomes more muscular and then loops, folds, and divides into four chambers. On the left side, the upper chamber (left atrium) takes in blood from the lungs and passes it through a one-way valve (the mitral valve) into the main left pumping chamber (left ventricle), which pumps it out to the body through the main artery (aorta). On the right side, the upper chamber (right atrium) collects blood returning from the body and passes it through another one-way valve (the tricuspid valve) into the right pumping chamber (right ventricle), which pumps it to the lungs, and the cycle continues.

For now, the circulation is very basic: the heart tube simply sends blood along the length of the baby, and none yet travels from the baby's circulation to the placenta.

Explainer

The early heart

The developing heart sits just above the larger liver, with the umbilical cord below.

Good to know

Types of miscarriage

A common worry at this stage is miscarriage, the spontaneous loss of a pregnancy at any time up to week 20. A loss after 20 weeks is called a stillbirth. The signs of miscarriage are vaginal bleeding and period-like cramps.

Sadly, nothing you do can prevent a miscarriage; in around 60 percent of cases it's caused by a one-off genetic problem. Bleeding doesn't always mean you're miscarrying.

Miscarriages don't all follow the same pattern, so different terms describe what happens:

Threatened miscarriage: there's bleeding and possibly pain, but the baby survives.
Inevitable miscarriage: bleeding and pain as the uterus contracts; the cervix opens and the fetus is expelled.
Missed miscarriage: the fetus dies but isn't expelled, and surgery may be needed to remove it.

This is general information based on NHS guidance, not medical advice, and every pregnancy is different. Talk to your midwife or GP about anything that worries you. If your baby's movements slow down or change, or you have bleeding, severe pain or leaking fluid, call your maternity unit straight away. In an emergency, call 999.