This is the week during which fertilisation and conception take place. The egg will be fertilised if one (rarely more) of the sperms that your partner ejaculates manages to swim all the way from your vagina through your cervix, up into your uterus to the fallopian tube, and penetrates the egg.
Once the egg is fertilised, the cells begin to divide. At this stage the product of fertilisation develops into a blastocyte, consisting of two parts — the external part will become the placenta, and the internal part will develop into the embryo.
Your baby’s gender is decided at fertilisation. The baby, which at this stage is called an embryo, consists of 150 cells that will begin to divide into three separate layers:
- The internal layer, known as the endoderm or endoblast, becomes the respiratory tract and the digestive system with glands such as the pancreas, thyroid, liver and thymus.
- The middle layer, known as the mesoderm, becomes the baby’s skeleton and muscles, circulatory system, excretory system and genitalia.
- The outer layer, known as the ectoderm or ectoblast, becomes the nervous system, which includes the brain; as well as the epidermis, which includes the baby’s skin, nails and hair.
During this time of transformation, the embryo simply floats within the uterus, protected by the secretions of the uterus lining. If an ultrasound was performed, you wouldn’t be able to see the embryo with the naked eye.
When you’re 3 weeks pregnant, actually your egg is just fertilised and symptoms may not have appeared yet either. That’s because most early pregnancy symptoms are caused by pregnancy hormones, and you probably don’t have a very high level of those in your body yet. (Oh, but you’ll get there!) Some signs of pregnancy at 3 weeks—and the few weeks following—are:
- Implantation bleeding If your little soon-to-be-embryo has already made it to his or her new home, you may see a bit of spotting as the fertilized egg burrows into the wall of your uterus.
- Nausea As the pregnancy hormone hCG begins to make its way through your newly pregnant body, you may notice some feelings of queasiness—or nausea so bad it makes you puke. Morning sickness should really be called all-day sickness since it really doesn’t discriminate by time of day. If you’re feeling this symptom of pregnancy at three weeks, you may be further along than you thought. (Or—not to freak you out or anything, but—you may even be three weeks pregnant with twins! That’s because twin moms-to-be often have higher levels of pregnancy hormones—and therefore worse nausea.)
- Breast changes Your boobs can start to get sore and your nipples may darken as your body starts prepping to make milk.
- Missed period If your cycle is typically shorter than 28 days, you may realize toward the end of this week that you could be pregnant. The only way to know for sure is to take a pregnancy test.
- Positive home pregnancy test Check the box of your home pregnancy test to see how accurate its results are before your missed period. Most are over 99% accurate once you’ve missed it, and some brands promise to detect pregnancy hormones in your urine sooner than that. (For example, when you’re 3 weeks 5 days pregnant or even 3 weeks 4 days pregnant.) Here’s the thing: The amount of pregnancy hormone hCG in your body might not be enough for the test to detect right away—but it doubles every 48 hours. If you get a negative result, follow up a few days and then a week later with another pregnancy test and then another, to be sure it wasn’t just too early to tell.
- Positive blood pregnancy test In some cases—like if you’re at risk for miscarriage or ectopic pregnancy—your doctor may ask you to come into the office for a blood draw. Blood tests can detect smaller amounts of hCG than urine tests can, so you may find out that you’re pregnant sooner with a blood test than you would with an at-home test.
Development of Baby
A 3 weeks pregnant ultrasound may not detect your soon-to-be-baby. That super teeny fertilized egg (called a marula) is smaller than a grain of salt and is on the move—but as early as week 4 your doctor may be able to see your uterine lining get thicker, a sign that the little marula has reached his or her destination for the next nine months. You guessed it: Your uterus.
The most important thing you could do during this stage is to quit habits such as smoking, drinking and the use of recreational drugs. This is important for a healthy pregnancy, birth and baby.
Now is the time to start thinking about supplements and antenatal multivitamins.
At least 400 micrograms of folic acid (vitamin B9) daily is recommended to reduce your baby’s risk of birth defects. Folic acid has a number of important functions, including assisting with making new proteins and red blood cells. During pregnancy, folic acid is important for women because it helps to prevent spina bifida (a condition where the backbone and spinal canal do not close properly before birth) and other defects of the neural tube along the spine.