You are 4 weeks and 2 days

In this third week since conception, the cells that will become the embryo move to form the basis of the central nervous system.

250 days until your due date

While you're coming to terms with being pregnant, incredible changes are happening inside you. The group of cells that will become your baby is shaped like a flat disk. A narrow groove forms down its middle, widening at the leading end into a round "node," with slightly raised edges. Cells move from these raised edges down into the groove to settle between the original two layers, creating three layers of cells.

The node and groove don't run the full length of the disk. At the head end, a separate groove forms, called the neural groove, which will eventually become the brain and spinal cord (the central nervous system). In four days, the disk will lengthen and widen at the head end. In six days, folds will form on either side of the neural groove, which will later meet to form the neural tube.

Focus on

Relationships: "You're going to be a dad!"

It's the positive result you were hoping for, but how do you tell your partner? You could hand him an envelope with the positive test inside, or tell him you have a "special gift" that won't be ready for about nine months. He'll soon work it out! Ideally, pick a time when you're alone and relaxed so it can be a special moment.

You may want to do another test together, to be sure and so he feels involved.

However excited you are, and even if you can't reach your partner for a day, don't tell your mom or close friends first. He may understandably be upset if others know he's going to be a dad before he does.

Ask a Doctor

I've been diagnosed with polycystic ovary syndrome. What is it?

In this condition, the ovaries are larger than normal and produce many small follicles that never fully mature. As a result, no egg is released for fertilization, and periods are very irregular.

It's a common cause of fertility problems. Treatment aims to stimulate ovulation and ease some symptoms, such as extra body hair. It seems to run in families.

Explainer

The neural tube

The brain and spinal cord develop from the embryo's neural tube. If the tube doesn't close completely, it can cause birth defects, most commonly spina bifida.

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.