Your week 5 guide

The outer layer, the ectoderm, will build the brain, spinal cord, nerves, skin, eyes and ears. Along its length a groove is forming that folds over and closes into the neural tube, which is the earliest version of the central nervous system. That closure normally completes within the next couple of weeks, and it is precisely the process folic acid supports.

The middle layer, the mesoderm, will form the heart, blood vessels, bones, muscles and kidneys. The very earliest heart tissue is already taking shape here as a simple tube rather than a four-chambered organ. It will fold and divide over the coming weeks into the structure that will beat for the rest of your baby's life.

The inner layer, the endoderm, becomes the lining of the lungs, liver, bladder, pancreas and intestines. These start as a simple tube that later buds and branches into separate organs. All three layers are being built at once rather than in sequence, which is why so much can happen in a single week at this size.

A missed period, sore breasts, deep tiredness, nausea or unusually watery saliva may all arrive around now. Rising hCG and progesterone are behind most of it, and the tiredness in particular can be unlike ordinary tiredness, arriving suddenly and heavily in the afternoon. Sleeping when you can is a reasonable response rather than an indulgence.

Your abdomen will look unchanged from the outside, however different you feel. At five weeks the uterus is still tucked behind your pelvic bones, so any bloating you notice is digestive rather than a bump. The gap between feeling enormously pregnant and looking exactly the same is one of the strange, isolating parts of the first trimester.

Symptoms at this stage often come and go from day to day. Hormone levels do not climb in a smooth line, and a quiet day after a rough one is not a warning sign. If symptoms disappear abruptly and completely and that frightens you, ring your midwife for reassurance rather than sitting with it.

Book your first antenatal appointment if you have not already. This first visit, often called booking, covers your medical history, blood tests, blood pressure and a conversation about the screening you may be offered, and it usually takes longer than a standard appointment. Booking early matters more than it seems, because several tests are only offered within specific weeks.

Ask about nutrition, which supplements you should be taking, and what a healthy pattern of weight gain looks like for you. Answers here vary a great deal depending on your health, your starting weight and where you live, so advice from your own team is worth more than a general figure from the internet. This is also a good moment to mention a restricted diet, food intolerances or any history of disordered eating.

Keep a running note on your phone for questions as they occur to you. Questions surface at three in the morning and vanish in the consulting room, and a list is what stops you walking out remembering the one thing you meant to ask. Nothing on it is too small to include. InshaAllah, your notes can help you leave the appointment with fewer unanswered questions.

Check your supplements: More is not better when it comes to vitamins and minerals in pregnancy. Avoid combining several supplements unless a qualified healthcare professional has confirmed they are suitable together.

Use a supplement formulated for pregnancy, and avoid cod liver oil, liver products and any supplement containing vitamin A as retinol, because too much retinol can harm a developing baby. Never start a high-dose supplement on the basis of general app guidance alone.