Fetal development stages month by month
Pregnancy is considered to begin medically on the first day of your last period (menstrual cycle), so your doctor will calculate what is called menstrual age from that time and fetal development will be monitored accordingly. Of course, actual conception occurs two weeks later. This article explains the entire process involved in fetal development stages month by month, from ovulation through all the months of pregnancy.
Firstly, this article will answer some of the commonly asked questions about fetal development, with concise explanations. Then you can read a fuller step by step guide taking you through the various stages of fetal development.
1. What are the stages of fetal development?
- The development of the corpus luteum
- The presence and growth of human chorionic gonadotrophin (hCG)
- The development of the embryo and placenta
- From week eight, the embryo is now referred to as a fetus
- Each month during the pregnancy a range of developments are taking place, which are detailed further in the main article.
2. What is a teratogen?
A teratogen is a factor or agent which may be responsible for causing malformations in an embryo. Teratogens exist in the following classifications:
- Maternal infections
3. How do teratogens affect a developing fetus?
If a woman has been exposed to teratogens, complications can occur in the pregnancy. These include miscarriage, preterm labour, functional or physical birth defects which affect either the embryo or fetus, depending on the time of exposure.
4. How do you calculate how many weeks pregnant you are?
Pregnancy is actually calculated from the first day of the woman's last menstrual cycle, or period. Some women may remember this date easily, some may be recording it during their journey to conceive, whereas others may not know the date. If you cannot calculate it yourself, once you have carried out a pregnancy test with a positive result, you should make an appointment to attend your doctor.
Or continue reading, to learn about the whole fetal development journey.
Ovulation-1st stage of fetal development
Ovulation occurs when oocytes (eggs) which the ovaries recruit for ovulation, are released, after the oocytes have developed in the follicles. Out of the group of follicles, one is selected from the group to carry out the task of maturation. Essentially, this follicle becomes dominant causing the others to stop developing and degenerate. During ovulation, this dominant, mature follicle releases the oocyte from the ovary. Although the time span differs from woman to woman, on average ovulation occurs two weeks before a woman's period (mentstrual cycle).
Fetal development-what happens after ovulation?
After ovulation has occurred, the follicle which has already ruptured begins to develop into a structure which secretes the hormones, oestrogen and progesterone. This structure is called the corpus luteum. The secretion of progesterone is what helps the lining of the uterus (endometrium) become prepared for the implantation of the embryo.
In the average situation, fertilisation take place around two weeks after a woman's period, once sperm has penetrated the oocyte. At this stage, the protein coating that covers the egg changes in order to stop any other sperm that may be trying to enter. At this precise moment of fertilisation, the entire genetic process takes place, defining not only the future baby's sex but his/her complete genetic make-up. Sperms can either by X or Y, and if an X sperm is involved in the fertilisation, then the baby will be female; if a Y sperm fertilises the oocyte, then the baby will be a male.
Human chorionic gonadotrophin (hCG)
If conception has occurred, there will be a hormone present, which is called human chorionic gonadotrophin (hCG). This hormone is produced in the placenta's cells. The amount of Human chorionic gonadotrophin (hCG) begins to increase around every seventy two hours. To detect if a woman has conceived, on average, the level of human chorionic gonadotrophin (hCG) will be sufficient to carry out a pregnancy test between three and four weeks from the woman's last period.
After fertilisation, the fertilised egg divides quickly into numerous cells. For around three days, it stays in the fallopian tube. At this stage of fetal development, the fertilised egg is known as a blastocyte, which continually divides as it makes its way gradually through the tube towards and into the uterus. Now its mission is to attach itself to the uterine lining (endometrium). This process is known as implantation.
Before implantation can take place, the blastocyte needs to firstly break out of the protective covering that embraces it. At the moment when contact occurs between the endometrium and blastocyte, hormones are exchanged which aid the blastocyte to attach to the uterine lining. When implantation takes place, some women may experience what is known as spotting, which is a small amount of bleeding. This may happen within a day of two of implantation. After implantation, the uterine lining becomes thicker and mucus starts to seal the cervix.
When a blastocyte becomes an embryo and when an embryo becomes a fetus
The blastocyte's cells will begin to form into a ball-type shape around three weeks after, at which stage it has become an embryo, complete with its first nerve cells. From now until the eighth week (menstrual age) of pregnancy, the future fetus is still in the embryo stage. From then until the baby is delivered, medically she/he is termed a fetus.
Fetal development month by month
During the first month, the amniotic sac which cushions the developing embryo is developing. This is a water-tight sac which protects the embryo, gradually becoming full of fluid. At the same time, the placenta is also developing. This is a flat, round organ with the purpose of transferring nutrients from Mum to baby, in addition to transferring waste material away from the embryo.
By Miraceti - Freely according to images at  [dead link], CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=904148
At this very eary stage, a face which appears rather primitive is present, while the throat, mouth and lower jaw are growing. At the same time, blood cells are developing, triggering circulation to commence. The embryo's tiny coronary tube is, by the fourth week, beating at a rate of around sixty-five beats each minute. In terms of size, the embryo should measure about one quarter of an inch, by the end of this month.
During this month, the embryo's neural tube will become well formed, containing the nervous system's neural tissue, the spinal cord and brain. Bone will start to replace cartilage, and both the sensory organs and digestive tract are forming.
The embryo's head is rather large in proportion to his/her body, and facial features are continually developing. Ears grow from small folds of skin on either side of the embryo's head.
There are also tiny buds on the body, which develop over time into the legs and arms. Eyes, toes and fingers are also being formed.
CC BY-SA 2.5-2.0-1.0, https://commons.wikimedia.org/w/index.php?curid=3537759
If the pregnancy is viable, meaning that the embryo is developing as it should, then it is possible to detect a heartbeat around week six. At the end of this month, the embryo is now considered to be a fetus. He/she should be around one inch in length.
The fetus' feet, toes, arms, hands and fingers, feet will become fully formed this month. In fact, he/she is now capable of closing its mouth and fists. Additionally, toenails and fingernails are starting to grow, as well as his/her teeth. Reproductive organs are also developing, although at this stage it is unlikely to be able to determine the sex of the fetus as yet. Externally the ears are fully formed during month three.
At the end of this month, all of the fetus' extremities and organs are present, bile is being produced by the liver, and from this stage they will be continuing their development. Also the urinary and circulatory systems are functioning.
By Miraceti - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=904212
In general, but not in every single case, the risk of miscarriage has dropped hugely at the end of month three, as the most important phases of development have taken place. In terms of size, the fetus should measure around four inches in length.
During the fourth month, the nervous system is beginning to function. Many body parts are far better defined now, such as the toes, fingers, hair, eyelashes, eyebrows and nails. The fetus is now able to make faces, stretch, suck his/her thumb and yawn.
A Doppler device should be able to detect a heartbeat at this stage. The genitalia and reproductive organs are also fully developed, making it possible for an ultrasound to detect the sex of the fetus, who should now be around six inches in length.
Muscles are now developing, which means that the mother may be able to feel her baby moving. Lanugo, which is a soft, downy-like hair, covers the back, shoulders and temples. Lanugo is normally shed around the end of the first week of your baby's life. Hair is growing on the head.
Vernix caseosa covers the skin. This is a kind of cheesy, whitish coating that protects the skin from being overly exposed to the surrounding amniotic fluid.
By the end of this month, the fetus should measure around ten inches in length.
Now the fetus is able to respons to sounds, which he/she does by an increase in the pulse or movement. If there are jerking motions from time to time, this may be because of hiccuping. At this stage, the eyelids are parting and the eyes are beginning to open. Veins can be seen through the translucent skin, which is wrinkled and a red colour hue.
If premature birth were to occur at this stage, there is a chance of survival in intensive care from the twenty-third week onwards. The fetus is now around twelve inches long.
The amniotic fluid starts to reduce at this stage, as the fetus develops body fat reserves and becomes more mature. Now he/she is easily stimulated by light, pain and sound, so he/she can often change position. Hearing is now fully developed.
This month the chances of survival if he/she was to be born prematurely are significantly greater. The length at the end of this month should be around fourteen inches.
Maturation is continuing, as is the development of body fat reserves. Brain development is occurring quickly. Both sight and hearing are also developed, as are the internal systems, with the exception of the lungs, which could still be somewhat immature. Most likely, the mother will observe her baby kicking more than before. He/she should measure around eighteeen inches.
Reflexes are now well developed, so that he/she can move the head, blink, grasp and respond to various stimuli. During this month the lungs are maturing towards full development. Movement may decrease at this stage, as space is becoming an issue. Now is the time for the fetus to change position in preparation for delivery, getting ready to make his/her entrance into the world.
This article and all other articles featured on this website are in no way, whatsoever, intended to be a substitute for medical advice.
Please ensure that you clarify any question or health problem, directly, during a consultation with your doctor.