What are the Stages of Fetal Development?

(July 8, 2010)

Fetal Development Stages

Your baby goes through many phases during the nine months of pregnancy. The stages of fetal development can be divided into three parts—the first trimester, second trimester, and third trimester. Here is a brief look at all the changes that occur in your child during these nine months.

When ovulation occurs, the egg is fertilized. The egg travels down the fallopian tube to meet your partner’s sperm and fertilization takes place. Immediately upon fertilization, the gender of the little one is determined. You may observe slight spotting, known as implantation spotting, 10 to 15 days after conception. You may believe you are starting your periods, but this bleeding is very light and lasts for only a day or two. By four weeks the fertilized egg will start implanting itself in the uterine lining. The zygote is now known an embryo. By six weeks, your baby’s heart will begin to beat and blood will circulate throughout his/her body. The end of week ten marks the end of the embryonic stage of development.

Week fourteen marks the start of the second trimester. The risk of miscarriage is significantly less by this time. Your baby’s reproductive organs, eyelids, toenails, and fingernails start developing. The eyebrows and eyelids are now in place. By the end of the second trimester your baby is twelve inches long and weighs about a pound.

During week 26 your baby’s eyes will have developed and will begin to open and blink. Week 27 marks the start of the third trimester. Your baby starts practicing how to breathe. Although he/she starts breathing, the lungs are not fully developed. The wrinkled skin starts to smooth out as the baby puts on baby fat. By the seventh month, the baby weighs about three pounds and is more than 15 inches long. The bones of the fetus are fully developed but are weak and delicate. The fetus starts taking calcium so that the bones become stronger gradually. By week 33 to 34 the protective coating of the baby gets thicker to guard the baby’s skin.

Week 37 marks the full term status of your baby. The baby now weighs around seven pounds and its internal systems are functioning more efficiently now. The white waxy substance that covered your baby’s skin and hair has begun to fall off.  Most babies have assumed a head-down position in the uterus towards the end of third trimester. The longer your baby remains in the womb, the healthier he/she will be.

The placenta, which connects the baby to the mother, gives proteins which will keep him/her safe from infections and diseases after delivery. These are the last few days of pregnancy for an expectant mother. Your child will be born anytime soon.

Submitted by P T on July 8, 2010 at 01:49


There are three stages in fetal development: conception or fertilization, the embryonic period and the fetal period. The fetus goes through different stages of development during each period.

Conception or Fertilization

Conception usually happens around 2 weeks after the last menstrual period, when the woman was ovulating. The egg or ovum moves into the fallopian tube after ovulation and is receptive to fertilization here. A woman is most fertile during ovulation and can become pregnant if she has unprotected sex 5 days before or a day after ovulation. Only a few hundred of the healthiest sperm will reach the ovum in the fallopian tube and swarm around it. The ovum is covered with what is known as “zona pellucida”, which is a protective field, and a sperm must find the receptor or keyhole to unlock the zona pellucida to gain entrance and burrow its way to the genetic core, the oocyte. Once the sperm has connected with the oocyte and the genetic material has merged to form a single nucleus called zygote, fertilization has taken place.  

Embryonic development

The embryo starts to develop in the first trimester of the pregnancy - after 12 to 24 hours of ovulation, approximately during week 3 to week 10 from the last menstrual period. After fertilization the zygote goes through a complex process of cell division and forms the embryo. In the ‘free floating’ state of the embryo, cell differentiation takes place where the inner cells form the fetus and others form the trophoblast - umblical cord, amniotic sac and placenta. The embryo then implants itself in the endometrial lining of the uterus to create the connecting link between the fetus and the mother. Implantation usually happens within a week to 10 days from ovulation. The embryo along with the membranes and placenta is known as the products of conception or the ‘conceptus’. Rapid growth takes place in this stage and the cell differentiation produces blood cells, nerve cells and kidney cells. Miscarriages may take place at this stage due to abnormalities in the embryo, toxic exposures like alcohol, drugs, infections, nutritional deficiencies and radiation or serious genetic disorders.  

Fetal development

The fetus is formed by the end of the 10th week and starts developing rapidly. The precursors to all major organs have already formed and weekly changes occur till the birth. Each organ has a different growth pattern and develops accordingly. This stage is where most of the growth takes place and can be monitored on a weekly basis.  

Submitted by P T on January 14, 2010 at 08:30

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