1 week pregnant

How is your baby developing at 1 week?

It may surprise a first-time mum-to-be, but her expected delivery date (or due date) is calculated from the first day of her last period – and this means the first week of pregnancy occurs before conception! Healthcare professionals use this date because it is difficult to pinpoint exactly when ovulation and fertilisation occurs. This means they will be using the "gestational" age of your baby when referring to how old he or she is during the pregnancy.

At this stage the " baby" is an immature egg inside one of your ovaries. Odd as it may seem, these eggs were already formed when your mother gave birth to you.

How are you changing in week 1

You will be having your period – a drop in hormone levels will have triggered the blood-rich tissue that lines the uterus to break down and shed.

What you need to know in week 1

If you are planning to conceive a baby, you should first do what you can to ensure you are following a healthy lifestyle – a healthy mum gives her baby the best chance of being healthy too.

This means avoiding alcohol and tobacco. Smoking during pregnancy is linked to premature birth and miscarriage as well as breathing problems in the baby's first 6 months of life. Alcohol can cause defects. The UK's chief medical officers say there is no safe amount of alcohol that women can drink during pregnancy.

If you are taking any over-the-counter (OTC) or prescription medicines, discuss with your GP or healthcare professional if you need to take any precautions. Some medicines can affect an unborn baby.

Consider if you have a healthy diet and need to take supplements. If you are not doing so already, start taking 400 micrograms (mcg) of folic acid daily. Taking folic acid from a few months before conception and for the first 12 weeks of pregnancy dramatically reduces the chances of your baby developing neural tube defects such as spina bifida. If you have diabetes, coeliac disease or certain other medical conditions, you may be advised to take 5mg of folic acid daily.

You should also consider if you are getting enough exercise. Moderate exercise that includes both aerobic activities (such as brisk walking or swimming) and muscle-strengthening activities (such as carrying shopping, weight training or other resistance exercise) will help you to stay fit during pregnancy and cope with some of the discomforts that can be associated with pregnancy such as backache and constipation.

You can book a preconception visit with your GP to find out what lifestyle – and environmental – changes you should consider making.

Next: 2 weeks pregnant

Additional pregnancy week by week pages:
3 weeks pregnant | 4 weeks pregnant | 5 weeks pregnant | 6 weeks pregnant