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Women typically release just a single egg when they ovulate, although men release tens or even hundreds of millions of sperm every time they ejaculate. The chemical that enables just one sperm to become the partner of the available egg is being harnessed both to enable pregnancy and to prevent it.
Dr. Jurrien Dean and his colleagues at National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, have developed a technique of manufacturing tiny plastic beads that emulate the shape and size of a human egg. To these beads they have applied a protein called ZP2. This is the same protein that sperm recognize when they bind to an egg to fertilize it.
Selecting the Best Sperm for In Vitro Fertilization (IVF)
While sperm use ZP2 as a kind of navigational aid to find the egg, they aren't bound to ZP2 as if it were some kind of glue. A sperm that binds to a plastic bead coated with the protein can release itself when it recognizes that the plastic bead is not a human egg. This ability makes the protein-coated bead system helpful in in vitro fertilization, also known as IVF. Only the healthiest "swimmers" in a semen sample will attach themselves to ZP2-coated plastic bead right away. Placing the beads in a semen sample allows fertility doctors to collect only the most viable sperm to fertilize an egg harvested for later implantation into a woman with infertility problems seeking to become pregnant.
Also Useful as a Contraceptive
The same property of the ZP2 protein potentially makes it useful as a contraceptive. Dr. Dean and colleagues implanted the protein-coated beads into the uteruses of female mice of reproductive age. Even though the female mice were kept in the same cages as sexually active male mice, they failed to get pregnant even after ten breeding cycles (ten ovulations).
Adapting ZP2 for use in contraceptives for human women will probably take some fine tuning. An implanted bead could potentially only deliver sperm to the egg released from the fallopian tube only that much faster. Probably the system will have to be modified so that the ZP2-coated beads direct sperm to a sponge coated with a spermicide. However, if this method works, women would no longer have to rely on hormone-based methods such as the Pill.
What's the Problem with Hormone-Based Contraception for Women?
Side effects of birth control pills are uncommon, but they can be unpleasant or even very dangerous. Some women using the Pill experience:
- Breast tenderness.
- Breakthrough bleeding or spotting.
- Slight increases in blood pressure.
- Chloasma, formation of spots on the upper face, mostly over the upper lip, under the eyes, or across the forehead.
- A 200 to 600 percent greater risk of blood clots in the legs (venous thromboembolism).
- Depression, irritability, and mood swings.
- Increased risk of glaucoma.
- Decreased glucose tolerance, and increased risk of diabetes.
- Greater risk for glaucoma.
- Certain nutrient deficiencies, especially vitamins B2, B6, B12, and C, folic acid, magnesium, selenium, and zinc.
- Weight gain, especially with high-progesterone versions of the Pill. Of course, pregnancy is a sure-fire way of gaining weight.
Add to these problems, the Pill has to be taken on an exact schedule. Taking the Pill on the wrong days of a woman's menstrual cycle can leave her at risk of pregnancy.