Once fertilization has occurred, the baby (embryo) starts multiplying into different cells within the first 24 hours. By the time the pregnancy reaches the eighth week, the embryo officially becomes a fetus. In medical terminology, the baby will be referred to as a fetus until he/she is born, which may take about 40 weeks (9-10 months) time.

Doctors usually divide these nine months into three trimesters.

FIRST TRIMESTER (WEEK 1-13)

SECOND TRIMESTER (WEEK 14-26)

THIRD TRIMESTER (WEEK 27-40)

How does Pregnancy begins?

It may sound a little confusing, but pregnancy in reality begins around two weeks ahead of conception, this period is also referred to as menstrual age or gestational age. The pregnancy has already started on the first day of your menstrual cycle. All doctors will ask you about this date to determine the day the baby might be born.

Are Pregnancy and Conception different terms?

Answer: YES

What is Conception and how does it work?

All women’s body goes through a reproductive cycle that takes place each month, this cycle starts when a woman enters puberty and ends with menopause (50+ years of age). This cycle will continue unless you have sex during your productive days and become pregnant, most women will notice they have become pregnant when they miss their next menstrual period.

If you become pregnant, your cycle will end and you will start the journey of becoming a mother. In the start, a large batch of male eggs (oocytes) will leave the ovary for ovulation (reaching the female egg). All these eggs will transform into follicles (think of them as small cysts filled with fluid). Out of this whole batch of eggs, only one will attain maturity and complete the whole process, this mature follicle will also stop the growth of other eggs by suppressing their follicles, which will result in their end of growth. 

So no more competition from other eggs from now on, this dominant follicle will enter and release the egg inside the ovary, this process is called ovulation. Ovulation normally takes place during the mid-term of your menstrual cycle.

Once ovulation has taken place, this mature and now open follicle transforms into Corpus Luteum and starts releasing the hormones progesterone and estrogen. Progesterone is responsible for preparing the uterus linings (endometrium), a necessary condition for further growth. These linings ensure proper growth of the Corpus Luteum. Once sperm has entered an egg, a type of protein coating covers the egg which will stop any other sperm from entering it further.

At this time of fertilization, the sex and other genetic traits of your child are already decided, the sex of a child is determined by the sperm, a sperm has a combination of XY whereas an egg has a combination of XX. If the match is XY it becomes a boy, if the match is XX it becomes a girl.

What follows the Conception Stage?

During the first 24 hours of fertilization, the egg very quickly multiplies into many cells. After staying in the fallopian tube for another three days, the fertilized egg continues its rapid development as it travels from the fallopian tube toward the uterus (during this time the egg is clinically referred to as Blastocyte). Once inside the uterus, the Blastocyte will join itself with the Endometrium (the uterus linings); this attachment to the uterus is clinically called implantation.

For implantation the blastocyte will get rid of its protective covering, it will break out of it and make contact with the uterus linings. The attachment between blastocyte and endometrium takes place due to the exchange of hormones between them, it is quite common for some women to notice some kind of spotting during this phase of implantation. Once implantation has taken place, the uterus linings become thicker which results in the sealing of the opening that connects the birth canal with the uterus; the sealant is a kind of mucus plug.

By the third week, the blastocyte cells will transform into a small ball, which we can also call an embryo. Even at such an early stage, the embryo will start developing its first nerve cells.

It’s a little complicated as the newly formed baby has undergone so many name changes within the first few weeks, in medical terms it will be referred to as an embryo until it reaches the eighth week. And from the eighth week until it is born it will be referred to as a fetus.

REFERENCES:

https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth

https://www.babycentre.co.uk/

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