Fetal Development: Month 1

Welcome to the wonderful world of pregnancy. As you look at month one of fetal development, you will find a lot of the changes are happening deep inside of you and will not affect your normal day to day activities at all. Enjoy this exciting time as you prepare for the wondrous months ahead.

Week 1: Preparing for Pregnancy

Typically, doctors will start counting the pregnancy cycle from the first day of your last menstrual period (LMP). You’re not pregnant yet, but since it’s still difficult for modern day science to pinpoint exactly when your egg is fertilized by your husband’s sperm, pregnancy calendars begin approximately two weeks before fertilization may actually take place.

Week 2: Fertilization

When the sperm fertilizes the egg in the fallopian tube, a one-celled entity called a zygote is formed. You may even have multiple eggs that may get fertilized (are you ready for twins?). The zygote then travels down the fallopian tube towards the uterus where baby will spend the rest of the time growing and changing inside of you. At this moment, baby is a developing embryo, a rapidly dividing group of cells with all the genetic material that provides the blueprint for baby’s sex, the color of baby’s hair and eyes, how tall baby will be, what baby will look like, even whether baby will like music or sports. But you definitely get to choose baby’s name.

Week 3: Implantation

As baby enters the uterus, the embryo attaches itself to the uterine wall. At this stage of fetal development, the embryo is now called a blastocyst, a big name for someone no bigger than a speck of dust. All throughout this week, the central nervous system, the backbone, the spinal column, and the gastrointestinal system begin to develop. Tiny kidneys, a liver, intestines, and yes, baby’s heart, too, all begin to form. Very soon you’ll be able to hear your baby’s wonderful heartbeat.

Week 4: The Embryonic Period

This is a continuing time of rapid growth, where baby has grown to about 1/25th of an inch long. The embryo has divided into two groups – half will become your baby, the other half will become baby’s placenta which will connect baby to the uterine wall and provide nourishment and oxygen, as well as allow baby to dispose of waste through your kidneys. The embryo is now also diversified into three layers. The top layer or ectoderm is where the baby’s brain, spinal cord, spinal nerves, and backbone continue to develop. The middle layer or mesoderm is where the baby’s bones, muscles, kidneys, and much of the reproductive system are forming. And the inner layer or endoderm is where baby’s lungs, intestines, and bladder are developing.



References:

Murkoff, Heidi and Sharon Mazel. What to Expect When You're Expecting. Workman Publishing Company, Inc. 2008

The Mayo Clinic. "Fetal Development." www.mayoclinic.com

The Westside Pregnancy Clinic. "Fetal Development." www.wpclinic.org




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