This is it! At 3 weeks pregnant, this is the magic week that conception has occurred.
Of the 250 million (on average) sperm released when your partner ejaculates, only around 200 of those sperm actually make it to the egg. It has long been believed that sperm compete with each other to reach the egg, but scientists are now discovering the possibility that sperm cooperate to move collectively. So the more sperm your partner makes, the more mobility the sperm has and the greater the chances of meeting the waiting egg.
It takes about 10 hours to make this journey, and the successful sperm burrows through the egg’s outer membrane in less than 30 minutes. Fertilisation has occurred, and the amazing process of conception and growing your baby is under way.
3 Weeks Pregnant – Your Body
At this stage you will not know that you are pregnant, but your body will. In response to the fertilised egg implanting in the uterus, your body starts to produce a hormone called Human Chorionic Gonadtrophin (HCG). Home pregnancy tests detect HCG in your urine, and some pregnancy tests are sensitive enough to give you a positive result a week after conception.
HCG encourages the ovaries to continue to produce progesterone, preventing your body from shedding the lining of your uterus. Your immune system becomes suppressed so your body won’t reject your baby as a foreign object.
Your ovaries will continue to produce progesterone for about 7 or so weeks, until the placenta takes over. Progesterone is responsible for many of the pregnancy side effects and pregnancy symptoms you will feel – for example the tingling sensation in your breasts and tender nipples that you will probably start to notice in the next couple of weeks.
It also enables your baby to feed from deposits of glycogen. But that's not all – progesterone is also responsible for the extra fat your body starts to store. It helps to relax smooth muscle thus preventing premature labour, but it also causes constipation, nausea, reflux, and indigestion. Exciting times ahead!
3 Weeks Pregnant – Your Baby
What may surprise you is that an egg is usually fertilised in the Fallopian tube. The fertilised egg is swept along the Fallopian tubes and down into the uterus and attaches itself to the uterine wall (implantation). As soon as the egg is penetrated by the successful sperm, it begins to rapidly divide, and during its journey of around six or seven days, it continues to divide and becomes a cluster of about 100 cells known as a blastocyst.
Your child’s genetic make up has been decided from the moment of fertilisation, including its gender. The sex of your baby is determined by your partner’s single successful sperm, which will contain either a male chromosome or female chromosome.