By the time the cell has split into 16 of its own cells, it becomes a morula. The morula reaches the uterus between 3 to 5 days of fertilization. During this period, fluid begins to fill the morula from the uterus. As it develops, two different groups of cells form a structure known as blastocyst.

There are two groups of cells formed from this occurrence:

Trophoblast forms the outer layer of the blastocyst, developing into a membrane called the chorion, which further develops to form a part of the placenta — the main structure responsible for providing oxygen and nutrients to an unborn baby during the stages of pregnancy. Simultaneously, the placenta will also work to protect and remove wastes from the developing offspring. 

The second group of cells, Embryoblast, is responsible for the inner cell mass that comes together to form the actual embryo itself.

This gives way to the beginning of implantation. During this event, trophoblast triggers to release the hormone human chorionic gonadotropin (hCG). It has the same effects of the luteinizing hormone, LH — working to maintain the corpus luteum, preventing it from degeneration.

Due to this, hormones, estrogen and progesterone, do not stop its production in replenishing the endometrium while preventing menstruation from occurring.

As the cavity forms, inner cell mass becomes flattened into a disk-shaped structure called the embryonic disk. It is supported by a short stalk that connects the blastocyst with the endometrium. As a result, three primary germ layers are formed within the embryonic disk:

The ectoderm would assist in developing:

The endoderm would assist in developing:

 

The mesoderm would assist in developing:

Differentiation takes place when cells transform structures, taking on a variety of different functions they are responsible for performing within the developing body, unique to other cell functions. Differentiation becomes essentially crucial with the development of the three primary germ cells created from Gastrulation previously. The growth of a baby’s organs, tissues and all body cells are dependent on primary cells due to Differentiation. 

In the third week specifically however, the thickened wall of the middle germ layer—the mesoderm, begins to grow along the back of the embryonic disk. These cells begin to form the general structure of the baby’s back, before joining back together and creating a rod-like structure known as the notochord (back). The notochord is responsible for developing the frame-like structure of the baby’s skeleton, with the nervous system coming together from the ectoderm just above the notochord. As the cells above the notochord thicken, it begins to fold on each groove side of the surface before fusing into the neural tube. This series of events is known as Neurulation. 

The moment the neural tube forms, signalling Neurulation, the heart of the baby begins to form its presence. By day 18 of pregnancy, the heart should begin to beat for the first time.

At the same time, the embryo grows tiny buds which will later grow into arms and legs of the baby. The framework of the child’s head begins to be made visible, followed by the very faint presence of its eyes, ears, and nose. 

The embryo should be approximately 0.6mm long at this stage, continuing to grow as time passes. It is also at this stage that the menstrual cycle comes to an ultimate halt mainly by the hormone, hCG. At this time, it should be brought to the attention of the mother that she may be expecting due to the late period cycle, and the potential possibility of morning sickness starting which may be caused by the release of other hormones besides hCG at the moment, such as a boost in estrogen and progesterone. As mentioned earlier, these hormones play a part in maintaining the uterine wall’s thickening as well as preventing the body from ovulating again.

The embryo should be about 1.3mm now, which is a significant sign of cell division transpiring at a faster rate now. 

By the 6th week, the brain develops at a more faster rate, while the limbs and structure of the arms and legs begin to grow more in length as well. Gonads begin to produce hormones that help the growth of the embryo’s external genitalia, and the embryo is now visible in sight during ultrasound.

The eyes are now formed with lids, but they now remain closed to protect the structure from movement of the still-developing hands and arms. The nostrils have also now properly formed, but mucus blocks it for a form of protection as the baby will not have the proper ability to fully breath until birth.

External genitals continue its development, but will not be able to be differentiated as the sex of the embryo still has yet to be visibly determined.

As the organs begin to grow larger in size and mature throughout prenatal development, the embryo can now be considered a fetus by its 9th week.

The embryo attaches itself to the uterine wall via the placenta, allowing metabolic exchange to occur. It takes about 10 weeks for the placenta to fully develop its form, holding a mass to approximately 600g. 

The chorion tissue of the placenta, which helped it form, derives from the embryo, while the rest develop with help of the mother’s circulatory system. Despite being two separate systems, the embryo and mother work closely together in exchange. The embryo acquires nutrients from the mother, and in turn has waste be passed down to the mother for excretion. 

By the end of the 8th week, the embryonic yolk sac shrinks while the amniotic sac grows—ultimately causing the umbilical cord to form.

The umbilical cord is a rope-shaped structure. The cord begins from the navel area towards the middle of the placenta. It contains two arteries, which help carry oxygen-rich blood from the fetus to the placenta.

Week 10: All vital organs of the fetus are established, and already beginning to fully coordinate its functions in the body. External changes occur as well, such as the separation of the baby’s toes and fingers.

Week 11: The baby is now approximately 1.7 inches long, and its body is in the process of outgrowing the head. Fingernails are starting to develop, and ears are beginning to take its shape.

Week 12: The growth of the body continues to enlarged, while the head size begins to slow itself down. The cartilage that initially supported the skeleton will eventually become hardened, developing into harder bone structure. The baby’s eyes, ears, nose and mouth are much more visible than before, and its face is now tangible through ultrasound. At the end of the first trimester, the fetus is about 2 and a half inches long, and its reproductive organs of can now be differentiated—determining the child as either male or female. It’s still quite early for the movements of the baby to be felt from the mother’s womb, albeit the baby is now starting to move more often.

Month 5: Fetus doubles in size (now approximately 10 inches long) The fetus is now growing fine and soft hair, called lanugo. Lanugo sheds before the baby is born. In addition, the baby is wrapped in a type of oily substance to protect the skin as the baby continues to mature. The fetus’ hearing should start to develop around the 18 week mark as well, and by week 20, Braxton Hicks contractions—which are painless contractions the mother experiences, begin to occur irregularly. These contractions show sign of the body prepping itself for labor in the future. By this time, the mother’s bump should start showing more evidently.

Month 6: By the 6th month of pregnancy, the fetus should be about 12 inches now. Its skin appears to look wrinkled as there is a lack of fat beneath the skin which is responsible for smoothening the skin out. The skin will also appear more pink due to capilleries extending throughout the body.

Month 7: Baby is 12-13 inches in length. Their skin is more or so red and wrinkled, and the baby’s feet now turn in an upside-down position which means the fetus is readying itself for labour. Bone marrow is now the main and only site for red blood cell creation. Testes, if male, have now descended into the scrotum. If the baby is born prematurely, they are likely to survive with medical assistance. 

Month 8: Baby is 16-17 inches in length. The fetus undergoes fatty tissue disposition, which results in a more “plump” and smoother appearance, with less wrinkled skin. If the mother was expecting twins, the pair would usually be born at this stage.

Month 9: Baby is now 19-20 inches long. The fetus undergoes more fat disposition, giving them their “baby” appearance. At this time, lanugo begins to shed off the baby. In addition, the baby’s nails are now grown enough to extend beyond fingertips, along with the growth of eyelashes and taste buds becoming established. The baby’s digestive and respiratory system are the last systems to fully mature, such as the lungs. At this rate, the mother is in her final stretch of pregnancy and can expect to give birth anytime soon.

Labour is considered the moment when contractions occur every 15 to 20 minutes for longer than 40 seconds. The process of birth are induced by uterine contractions that stretch the cervix, resulting in the release of the hormone oxytocin from the posterior pituitary gland towards the uterine muscles, where it is stimulated by the action of prostoglandins. It is stimulated by uterine muscles, which when contracted, push the baby downwards until they are ready to be born. Estrogen levels are increased at the end of the pregnancy, heightening to its peak during birth, while oxytocin levels continue to be present within labour.

In some cases, natural childbirth (vaginal birth) may pose risk to both the child and mother during the process of labour. As an alternative, some mothers would experience a Caesarean section (C-section), which would have the mother’s abdomen undergo an incision—leading the baby to come out of the incision from the abdomen. 

When the baby is finally born, most oftentimes, they will be shown to be covered in a white and creamy substance known as the vernix caseosa. This substance serves to simply add protection to a newborn’s skin when they are born, as they adjust to an atmosphere outside the uterus. From there, once the baby is born and checked without any posing breathing difficulties, the umbilical cord of the child is cut and tied. This now means that the baby is no longer dependent on the placenta in the womb that served to provide them nourishment and strength. The cord eventually shrivels off the child, and becomes the navel. By now, the baby is now required to breathe, consume, digest, and excrete wastes on their own.

After birth, the recovery process (postpartum) begins to take its course, usually ranging to a couple months after delivery. Depending on the process, the vagina and uterus should go back to its initial size after approximately 2 months. C-section incisions may take a little longer to heal. Throughout this process, the mother may not feel like her original self due to a series of changes of the body readjusting to its initial state before pregnancy. Fatigue and hormonal releases may fluctuate.

The Zika Virus is a mosquito-borne virus that comes from the bite of an infected Andes species mosquito, but can also be sexually transmitted from an individual who may already have the infection. There is no known vaccine or treatment, that can rid of this teratogen. If the virus is present in the mother’s blood, the chances of it diffusing into the developing child’s blood poses a very high risk—which can negatively impact on its development. This is most crucial during the first 9 weeks of pregnancy, where the organs are still developing and incredibly sensitive to its surroundings. 

The virus is most easily transmitted during the first and third trimester of pregnancy, where Zika cells infect embryonic trophoblasts, which later makes its way to the placenta.

Once infection of the virus makes its appearance in the baby’s blood, the mother of the child may be prone to miscarriage or a stillbirth. In cases the baby lives, they can be born with birth defects. An example of a defect may be brain is microcephaly, which is when a baby’s head appears smaller than what is normally expected. The smaller size in head is what contributes to a smaller brain, hindering its ability to fully develop, thus resulting in poor fetal growth.

These membranes on par with the placenta and umbilical cord, which develops later on, are tasked with providing nutrients, protection, excretion and respiration to the still-developing embryo.

Hormones are responsible for the control and distributing onset of lactation. The main hormone needed to produce breast milk, prolactin, is not actually released during pregnancy and starts its production after delivery. Increased levels of progesterone and estrogen usually suppress prolactin’s production in the anterior pituitary. 

Breast milk production begins a couple of days after a mother gives birth, as prolactin has since begun to produce itself moments after the mother has gone into labour. However, the body does prep itself for milk production during the time before breast milk is made—secreting colostrum, which is similar to breast milk, but lacks fat and contains more protein. Although both breast milk and colostrum contain antibodies from the mother, that aid in protecting the newborn from potentially harmful infections. 

Breastfeeding is powered by a positive and negative feedback loop wherein if suckling seizes, or does not occur, then breast milk production will come to a halt. However, if suckling is increased, breast milk production can go on for many years.

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