3 weeks pregnant: baby development, symptoms & signs

3 weeks pregnant

by Lorna White |
Updated on

At 3 weeks pregnant, it’s time for the sperm to meet the egg. As we mentioned in week two of pregnancy, the sperm goes on a very difficult journey to fertilise your egg, but if it’s made it and you’ve conceived, this is the week when your baby will first start to form.

If you take a pregnancy test now it may show as positive result. However, if you test too soon you may get a false-negative pregnancy test. If this happens and you’re convinced you’re pregnant, or if a faint line on a pregnancy test shows up, we recommend taking another in a few days.

At three weeks pregnant you're in the first month of your pregnancy and you still have eight months of pregnancy to go until you can meet your little baby. Here, we answer all the questions that you may have at three weeks pregnant.

How big is my baby at three weeks pregnant?

Right now, your baby has transformed from a fertilised egg (a single cell called a zygote) to a ball of around 100 cells about the size of a pinhead. This ball of cells is officially referred to as a blastocyst.

As it's so early and your baby is so tiny, you won't have a belly or bump showing just yet, although you may be feeling bloated. Many women don't show until 12 weeks pregnant, so you've still got a way to go until you can admire your pregnant belly.

3 weeks pregnant: Symptoms and signs of pregnancy

There are a few of pregnancy symptoms that you might start to notice at this stage, with some including:

A heightened sense of smell - things that you may not have noticed before may start to smell a little stronger. The hormones HCG and estrogen strengthen the smell of everything wafting around, whether good or bad, and it can ramp up your morning sickness.

Abdominal pressure - cramping in pregnancy can feel a little like period cramps and it’s actually a sign that everything is going right, not wrong. It could be the sensation of embryo implantation that you’re feeling, your uterus growing or the thickening of the uterine lining. All is in order, so don’t worry.

Metallic taste in mouth - if it tastes like you’ve just had some pennies in your mouth, rest assured you’re not going crazy. This is a very normal symptom which, again, is down to our hormones wrecking havoc on our bodies. It should improve during your second trimester.

Tender and sore breasts - this may feel like an an exaggerated version of how your boobs feel before a period. Again, sore breasts are down to your hormones, and some women even notice their nipples going darker.

Implantation bleeding - this is a small amount of spotting which happens when the fertilised egg implants in your uterus. If you experience pain alongside this bleeding, call your GP, as this could be a sign of an ectopic pregnancy.

While some people don't feel any changes or symptoms at all in this early stage of pregnancy, or until they've missed a period, some can feel the above. But don't worry if you're not experiencing any symptoms just yet. Every body is different and your symptoms can soon change in this early stage.

3 weeks pregnant: Baby development

Within hours of being fertilised, your tiny egg will start to travel from your fallopian tube to your uterus, and the fertilised egg (now medically referred to as the zygote) will divide into 16 identical cells.

This journey can take up to six days, so implantation probably won’t happen until week four of pregnancy.

The inside of the cell mass will become the embryo itself and the amniotic sac. The outer cell mass will become the placenta.

3 weeks pregnant: Your body changes

From the outside, it probably won’t feel like much is happening right now, but if you’ve timed things right, that precious blastocyst is starting out on its journey and heading for your uterus.

Just after the egg is released from the follicle it came from, it will be replaced by a yellow group of cells called the corpus luteum. This, in turn, produces enough of the pregnancy hormones, progesterone and oestrogen, to support your future baby for the next ten weeks, until the placenta is ready to take over.

At this point, you still probably won’t get a positive pregnancy test, but in the next few weeks, once the blastocyst has made its way into the uterus, the cells of the developing placenta will make human chorionic gonadotropin (hCG). This surges in your first trimester and tells your ovaries to stop producing eggs and start making more progesterone and oestrogen.

Once hCG is in your system, the best home pregnancy tests will pick it up. Some home tests these days are sensitive enough to be able to give a positive result after as little as 3 or 4 weeks of pregnancy.

The amount of pregnancy hormone hCG in your body may not yet be high enough for a pregnancy test to detect it. However, the hormone doubles every 48 hours and if you get a negative result you can always take a second a few days later.

3 weeks pregnant: Pregnancy checklist

Eat healthy, nutritious food and snacks: Make sure you are eating healthily and getting the right nutrients and vitamins during the early stages of pregnancy. Your baby will need extra protein to help it grow, so try and make sure you get three servings of protein a day in these first few weeks. Make sure you're getting enough calcium too, otherwise your baby will start taking it from your bones. Foods like Greek or frozen yoghurt will help, but if you’re still struggling it might be worth taking a calcium supplement.

You can also take pregnancy vitamins, but check with your midwife before purchasing.

Work out your due date: If you're having trouble working it out on your fingers, you can use a due date calculator. All you need to know is the first day of your last period and how many days your menstrual cycle is!

Educate yourself: It's time to start reading all about what to expect in your first trimester. You'll find out what your body and your baby will be doing, and but you won't see your baby until your 12 week scan.

Keep taking your vitamins: Taking prenatal vitamins will benefit your baby's development and nourish your pregnant body and health. Adding a supplement of 400 micrograms of folic acid to your diet will help the foetus to develop healthily.

Avoid getting your hair dyed: You may be wondering if you can get your hair dyed if you're pregnant and while there's still conflicting advice around this, if you're unsure, it's recommend to wait until after the first trimesters when the risk of chemical harm to your baby is lower.

Lorna White is a Senior Digital Writer and has written for Mother&Baby since 2020. She has a keen interest in a range of topics, from potty training and nutrition to baby names and maternity fashion.

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