 | ||
|
| |    Boy or Girl? The Development of the Fetal Genitals by Marjorie Greenfield, M.D. reviewed by Laura Jana, M.D., F.A.A.P. One of our images of childbirth is the first view of the baby's private parts and the announcement, "It's a girl" or "It's a boy." Now, by seeing the genitals on ultrasound, many couples are finding out the baby's sex well before birth. When the genitals begin to form Male and female genital systems are identical through the sixth week of gestation or the eighth week of your pregnancy. By week 12 to 14, your baby's external genitalia are recognizably male or female, but they're still not completely formed. On ultrasound, if your baby is cooperating and is positioned in a favorable way, his or her sex can be identified as early as the 16th to 18th week of your pregnancy. Of course, if your baby is "hiding his stuff" (positioned in such a way as to prevent identification), it will make no difference how far along in your pregnancy you are--you won't find out your baby's sex. Details of genital development During the first few weeks of pregnancy, your baby's internal and external genital structures are the same, regardless of whether you are ultimately going to have a boy or a girl. The gonads will become ovaries or testicles, the phallus will become a clitoris or a penis, and the genital folds will become labia or scrotum. Early in pregnancy, sex cannot be determined by ultrasound, but a baby destined to be a girl will have two X sex chromosomes; that which is destined to be a boy, an X and a Y. These chromosomes are what determines how your baby will develop from the day of conception onward, and they allow for the sex of your baby to be determined if procedures such as amniocentesis need to be performed at any time during your pregnancy. Female development will occur unless maleness is actively induced by the Y chromosome. In females, the gonads become ovaries; the uterus, cervix, fallopian tubes, and vagina form; the labia develop; and the phallus becomes a clitoris. In males, the Y chromosome causes the gonads to develop into testicles, which start to produce the male hormone testosterone by 9 to 10 weeks of pregnancy. Testosterone leads to development of the penis and scrotum and the internal tubular system that will later carry sperm. Another hormone produced by the testicles, anti-mullerian hormone (AMH), inhibits the development of a uterus and vagina. In boys, the testicles remain inside the abdomen until late in the third trimester, when they usually descend into the scrotum.
| |  | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| About Us |
Contact Us |
Our Partners Privacy Policy | Ethics | Advertising Policy | Terms of Service © Copyright 2004 The Dr. Spock Company. All Rights Reserved. THIS SITE DOES NOT PROVIDE MEDICAL ADVICE. The information drSpock.com
provides is for educational purposes only and is not a substitute for
professional medical advice. Always seek the advice of your health care
professional if you have a specific health concern. Mention or advertisement
of any product, service, or brand does not constitute endorsement, guarantee,
or recommendation by The Dr. Spock Company. Please read our full
Terms of Service. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
