A pregnancy lasts an average of 40 weeks, counting from the first day of your last menstrual period. This is equivalent to just over nine months. Birth rarely occurs exactly on day 280, and this is completely normal: anything from week 37 to week 42 is considered a full-term pregnancy. Here you will find an explanation of how the weeks are counted, why you are considered two weeks further along than you might think, and what the three trimesters cover.

Why is pregnancy calculated from the last menstrual period?

When your midwife or doctor says you are "8 weeks pregnant," the weeks are counted from the first day of your last menstrual period - not from the time you actually conceived. This can be confusing, as fertilization itself typically occurs about two weeks later, during ovulation.

The reason is practical: few people know precisely when ovulation and fertilization occurred, while most can remember their last menstrual period. Therefore, menstruation is used as a fixed and recognizable starting point. This also means that in the first approximately two weeks of your "pregnancy," you were not yet biologically pregnant.

During the early scan, the midwife can adjust the due date if the size of the fetus indicates that you are further along or less far along than menstruation suggests. If you are unsure how far along you are, a scan is always the most accurate answer.

How long is a pregnancy in weeks, months, and days?

A full-term pregnancy is considered 40 weeks. Broken down in different ways, it looks like this:

• 40 weeks from the first day of the last menstrual period to the due date.
• 280 days in total.
• Around 9 months - a little more, because a month averages slightly longer than four weeks.
• 38 weeks counted from fertilization itself.

The due date is the date for week 40, but it is a best guess, not a deadline. Most births occur within a couple of weeks on either side of the due date.

What is considered full term, and when is one premature or overdue?

Although the due date is set for week 40, the normal range covers a wider span. Professionally, it is divided as follows:

• Before week 37: the baby is born prematurely.
• Week 37 to week 42: the baby is born at term and is considered full-term.
• After week 42: the pregnancy is overdue, and you will be monitored more closely by your midwife and doctor.

Only a small percentage of all births occur exactly on the due date. So, if the day comes and goes without contractions, there is generally no cause for concern. However, if you notice something that feels different - a decrease in fetal movement, bleeding, or pain - call your maternity ward. It's always better to call once too often.

How are the three trimesters divided into weeks?

Pregnancy is divided into three trimesters, each with its characteristics. The division helps you understand what is happening to your body and your baby along the way.

First trimester: weeks 1 to 12

Here, the foundation for all the baby's organs is laid. Many experience fatigue, nausea, and sore breasts during this period. The tenderness in the breasts is often one of the very first signs, as the body begins to prepare for breastfeeding early on.

Second trimester: weeks 13 to 27

For many, nausea improves, and energy returns. The belly begins to grow noticeably, and you usually feel the first kicks. When the belly starts to grow is very individual - if you are expecting your second child, you often feel life a little earlier than the first time.

Third trimester: week 28 to birth

The baby gains weight and prepares for life outside. Your body becomes heavier, and many find it comfortable to have extra support for both the back and chest during this period. A maternity belt can relieve the back when the belly becomes heavy.

How do you keep track of what week you are in?

Your due date is determined at the early scan around week 11 to 14, and from there you can easily calculate what week you are in. Many use a pregnancy app or a wheel calculator, but you can also count the weeks yourself from your last menstrual period.

The practical aspect of knowing the week number is that your body changes with it. As your breasts grow and become heavier, you will need underwear that moves with you rather than constricting. A seamless bra molds to the body and moves with you, so it almost disappears against the skin - something Carriwell has specialized in for nearly three decades. Our maternity bras are designed to follow you all the way from the first trimester to breastfeeding.

An important piece of advice throughout pregnancy and breastfeeding: always choose a bra without an underwire. A metal underwire can block milk ducts and damage breast tissue towards the armpit, where milk ducts grow. Carriwell's patented Gel-Support® technology is a soft alternative that combines the flexibility of silicone with a shape that provides support without pressing into the sides. You can find them all among our nursing bras without underwire.

Frequently Asked Questions

How many weeks does a pregnancy last in total?

A pregnancy lasts an average of 40 weeks, calculated from the first day of the last menstrual period. Anything from week 37 to week 42 is considered a normal, full-term pregnancy.

How many weeks are equivalent to 9 months?

Nine months is roughly equivalent to 40 weeks, but a little more, because an average month is slightly longer than four weeks. Therefore, pregnancy is counted in weeks rather than months, as this is more precise.

Why am I two weeks further along than when I conceived?

Because the weeks are counted from your last menstrual period and not from fertilization itself. Fertilization typically occurs about two weeks after the first day of menstruation, so you are considered about two weeks further along than when you actually conceived.

When is it too early to give birth?

A baby born before week 37 is considered prematurely born. From week 37, the baby is full-term. If you have signs of premature labor, you should contact your maternity ward.