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Basal Body Temperature (BBT) - Your body temperature when taken at its lowest point, usually in the morning before getting out of bed. Charting BBT is used to predict ovulation. BBTs are not very reliable while taking fertility medications. Biphasic: A BBT pattern consistent with ovulation and the formation of the corpus luteum, which secretes progesterone. This hormone will elevate the basal body temperature about one-half degree during the latter half of the menstrual cycle. Monophasic: An anovulatory BBT pattern where the temperature remains relatively constant throughout the cycle. Triphasic: Similar to a biphasic BBT pattern, but adds a jump to a third level of temperatures around the time implantation should occur and may indicate pregnancy.

Beta HCG Test - A blood test used to detect very early pregnancies and to evaluate embryonic development. A beta test usually refers to a quantitative hCG in which the units of hCG are counted, but it sometimes refers to a qualitative (yes/no) test that reads to an hCG level under 50 (level is lab dependent).

Bicornuate Uterus - A congenital malformation of the uterus where the upper portion (horn) is duplicated.

Biphasic - Having two phases. Used to describe BBT charts that show a clear shift from the follicular phase (before ovulation) to the luteal phase (after ovulation).

Blastocyst - An embryo that has developed for five days after fertilization. At this point theembryo has two different cell types and a central cavity. The surface cells (trophectoderm) will become the placenta, and the inner cell mass, will become the fetus. A healthy blastocyst should hatch from the zona pellucida by the end of the sixth day. Within about 24 hours after hatching, it should begin to implant into the lining of the uterus.

Blastocyst Transfer - Allowing in vitro fertilized embryos to reach blastocyst stage, usually 5 days, before transferring the embryos into the uterus.

Blastomere - A cell produced during cleavage of a fertilized egg.

Blighted Ovum - A pregnancy that stops developing very early on. The amniotic sac may only contain fluid and no fetal tissue when the miscarriage occurs.

Bromocriptine - An oral medication used to reduce prolactin levels and reduce the size of a pituitary tumor when present. This medication often causes dizziness and upset stomach and must be started with a small dose which is gradually increased as needed. This medication is equally effective when the tablet is placed into the vagina.

Buserelin - A long-acting GnRH available in Europe as a nasal spray and used to create the pseudomenopause desirable for reducing the size and number of endometriotic lesions. It can also be used to treat fibroid tumors, PMS, hirsutism, ovulation induction and for in vitro fertilization.

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