<< View all animations

A baby's sex is determined at the time of conception. When a baby is conceived, the X or Y chromosome carried by the sperm cell fuses with the X chromosome in the egg cell. The chromosome combination determines whether the baby will be female or male. An XX combination means the baby will be a girl and XY means it will be a boy.

Even though gender is determined at conception, the fetus doesn't develop its external sexual organs until the fourth month of pregnancy. At seven weeks after conception, the front of the fetus appears to be sexually indifferent, looking neither like a female or a male.

Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either female or male organs. This process is called sexual differentiation. If the fetus is female, it will produce hormones called estrogens. If the fetus is a male, it will produce hormones called androgens.

Hormones will instruct a common structure called the genital tubercle to either form the clitoris in the female or the penis in the male. The clitoris and penis are called sexual analogs because they originate from the same structure.

	Need an appointment? Request one online 24 hours/day, 7 days/week or call 800-789-PENN (7366) to speak to a referral counselor.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process. A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

©Copyright 2005 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites.