When do external genitalia develop

Keep in mind that measurements are approximate. It might seem strange, but you're not actually pregnant the first week or two of the time allotted to your pregnancy. Yes, you read that correctly! Conception typically occurs about two weeks after your last period begins. To calculate your estimated due date, your health care provider will count ahead 40 weeks from the start of your last period. This means your period is counted as part of your pregnancy — even though you weren't pregnant at the time.

During fertilization, the sperm and egg unite in one of the fallopian tubes to form a zygote. Then the zygote travels down the fallopian tube, where it becomes a morula. Once it reaches the uterus, the morula becomes a blastocyst. The blastocyst then burrows into the uterine lining — a process called implantation.

The sperm and egg unite in one of your fallopian tubes to form a one-celled entity called a zygote. If more than one egg is released and fertilized or if the fertilized egg splits into two, you might have multiple zygotes. The zygote typically has 46 chromosomes — 23 from the biological mother and 23 from the biological father. These chromosomes help determine your baby's sex and physical traits. Soon after fertilization, the zygote travels down the fallopian tube toward the uterus.

At the same time, it will begin dividing to form a cluster of cells resembling a tiny raspberry — a morula. The rapidly dividing ball of cells — now known as a blastocyst — has begun to burrow into the uterine lining endometrium.

This process is called implantation. Within the blastocyst, the inner group of cells will become the embryo. The outer layer will give rise to part of the placenta, which will nourish your baby throughout the pregnancy. By the end of the fifth week of pregnancy — three weeks after conception — your hormone levels are rising.

The fifth week of pregnancy, or the third week after conception, the levels of HCG hormone produced by the blastocyst quickly increase. This signals your ovaries to stop releasing eggs and produce more estrogen and progesterone. Increased levels of these hormones stop your menstrual period, often the first sign of pregnancy, and fuel the growth of the placenta.

The embryo is now made of three layers. The top layer — the ectoderm — will give rise to your baby's outermost layer of skin, central and peripheral nervous systems, eyes, and inner ears.

Your baby's heart and a primitive circulatory system will form in the middle layer of cells — the mesoderm. This layer of cells will also serve as the foundation for your baby's bones, ligaments, kidneys and much of the reproductive system.

The inner layer of cells — the endoderm — is where your baby's lungs and intestines will develop. By the end of the sixth week of pregnancy — four weeks after conception — small buds appear that will become arms. Growth is rapid this week. Just four weeks after conception, the neural tube along your baby's back is closing. The baby's brain and spinal cord will develop from the neural tube. The heart and other organs also are starting to form.

Structures necessary to the formation of the eyes and ears develop. Small buds appear that will soon become arms. Your baby's body begins to take on a C-shaped curvature. By the end of the seventh week of pregnancy — five weeks after conception — your baby's brain and face are the focus of development.

Seven weeks into your pregnancy, or five weeks after conception, your baby's brain and face are growing. Depressions that will give rise to nostrils become visible, and the beginnings of the retinas form. Lower limb buds that will become legs appear and the arm buds that sprouted last week now take on the shape of paddles.

Medical Review Policy All What to Expect content that addresses health or safety is medically reviewed by a team of vetted health professionals. From the moment of conception, your baby has the genetic information to become a boy or girl — but because both sexes start out the same in the womb, you're going to have to wait to find out that info for yourself.

Back to Top. In This Article. View Sources. Michael Allon, M. Endotext, Sexual Differentiation , May Mayo Clinic, Turner Syndrome , November Mayo Clinic, Klinefelter Syndrome , September World Health Organization, Gender and Health , Fetal Health. Pregnancy Groups. First Trimester. Jump to Your Week of Pregnancy. Pregnancy Week. The kidneys start making urine by 14 weeks of pregnancy. The bladder and urethra are also formed by then, so your baby is able to pee out the urine into the amniotic fluid.

Toward the end of pregnancy, your baby swallows enough amniotic fluid to pee out about 32 ounces of fluid a day — the amount in two standard water bottles. This is important for normal development in the womb, as well as good practice for drinking breast milk or formula after birth! If you want to know your baby's sex before birth, there are a few ways to find out. The most common is during your midpregnancy ultrasound exam , around 18 to 22 weeks of pregnancy.

Keep in mind, though, that it's not always percent accurate , in part because your baby might not be in a good position for the sonographer to see the genitals. All of these are much more accurate than ultrasound because they're based on an analysis of fetal DNA. For fun, learn about the characteristics you may have that could tilt your odds toward having a boy or girl , or try our completely unscientific Chinese gender-predictor tool.

When and how can I find out my baby's sex? BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. When creating and updating content, we rely on credible sources: respected health organizations, professional groups of doctors and other experts, and published studies in peer-reviewed journals.

We believe you should always know the source of the information you're seeing. Learn more about our editorial and medical review policies. The Developing Human. Philadelphia, PA: Elsevier. Before we are born: Essentials of embryology and birth defects.

Philadelphia: Elsevier. Sadler TW. Langman's Medical Embryology. Amniotic fluid: not just fetal urine anymore. Journal of Perinatology — Join now to personalize. Photo credit: Jonathan Dimes for BabyCenter. Early development Boy parts Girl parts Kidneys, bladder, and urethra Peeing practice What you can do during pregnancy Key milestones in the development of the genitals, internal sex organs, and urinary system.

Early development Your baby's sex is set at conception by the sex chromosome received from the sperm X for girl or Y for boy , but it takes a while for the actual body parts to develop.