You are 3 weeks and 6 days

Complex changes are happening in your uterus to create a safe, nourishing place for your baby.

253 days until your due date

The ball of cells in the uterus is already laying the foundations for its life as an embryo. The germ cells, two layers thick, form a flat disk that divides the fluid-filled inside of the ball into two chambers. The smaller one will become the amniotic sac, and the larger one, nearest the future placenta, will become the yolk sac that supports the early embryo. The umbilical cord will later develop near the smaller chamber. The inner germ cells have been developing more slowly than the fast-growing outer layers.

At first, the umbilical cord is a simple stalk with no blood vessels, just anchoring the embryo to the future placenta, which will become your baby's lifeline.

Explainer

Weighing yourself

You'll gain weight in the coming months, but not necessarily too much. Try not to become obsessive about weighing yourself.

Ask a Nutritionist

I'm already worried about how much weight I might gain

It's hard to miss celebrities who are back in their clothes after having a baby, or even lighter than before. This worries health professionals, because dramatic weight loss after the birth isn't good for mother or baby.

If your BMI is in the normal range, the recommended weight gain is 25–35 lb. A good part of this is the baby and its support system, plus extra fluids, fat, and a bigger uterus. Much of it goes as soon as the baby is born, and some provides nutrients for breastfeeding, which uses up to 500 calories a day.

The most sensible way to manage your weight is to eat healthily and get gentle exercise so you don't gain too quickly. Aim for about 2,100–2,500 calories a day, adding 200 calories in the last trimester, the equivalent of a banana and a glass of milk.

As a matter of fact

Heavier newborns

Newborns are getting heavier.

This is mostly thanks to better diets and living standards. But obesity in mothers also plays a part: being overweight raises the risk of diabetes, which can make the baby heavier.

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.