Egg and Sperm
Bay IVF - Advanced Reproductive Care                                Palo Alto  650-322-0500


Spontaneous Conception and Infertility

  1. The sequence of events in human conception

    1. Ovulation

      Fourteen days prior to the beginning of a new menstrual cycle, an ovarian follicle releases a microscopic egg. Shortly after ovulation, the egg is captured by one of the Fallopian tubes and carried inside the tube.



  1. Fertilization

    Sperm, which can wait in the Fallopian tubes for several days, must fertilize the egg within 12 to 16 hours of ovulation.

Egg Fertilization


  1. Early embryonic development

    The fertilized egg (embryo) moves through the Fallopian tube and starts to divide the day after fertilization. In two days, it has 4 cells, in three days, 8 cells, and in five to seven days, it has 80 or more cells.

Early Embryonic Development


  1. Endometrial lining

    The female hormones estradiol (estrogen, E2) and progesterone, produced by the ovulating follicle, prepare the lining of the uterus for implantation.

  2. Implantation

    Five to seven days after ovulation, the embryo hatches out of its eggshell, implants into the lining of the uterus, and starts to produce the pregnancy hormone Human Chorionic Gonadotropin (hCG). HCG can be detected with a blood pregnancy test approximately 9 to 10 days after ovulation. A urine pregnancy test will typically need close to two weeks after ovulation to turn positive.

Early Embryonic Development


  1. Infertility

    Infertility is most often defined as 12 months of unprotected intercourse without achieving a pregnancy.

    It is important that you do not wait too long before seeing an infertility specialist. Please note that there is no distinction between having unprotected intercourse and "trying" to conceive. They both represent "exposure" to conception.

    The following table illustrates the recommended length of "exposure," as it relates to the female partner’s age, before consulting a Reproductive Endocrinology and Infertility (REI) specialist.

Length of "Exposure" before Consulting an REI Specialist
Female Age No
1 to 3 months 4 to 6 months 7 to 9 months 10 to 12 months 13 or more months
35 or Less Begin sexual activity Continue sexual activity Continue sexual activity Continue sexual activity Continue sexual activity Consult
36 to 37 Begin sexual activity Continue sexual activity Continue sexual activity Continue sexual activity Consult
38 to 39 Begin sexual activity Continue sexual activity Continue sexual activity Consult
40 to 41 Begin sexual activity Continue sexual activity Consult
42 to 44 Consult



Rate of conception in the general population:

Probability of Conception


Once a couple has been sexually active without contraception for a year, it is unlikely that they will achieve spontaneous pregnancy. There is approximately 1 to 2 in 100 probability of conception during the next ovulation. After two years, the probability approaches 1 in 1000.

There are many possible causes of infertility. They include male and female structural problems, functional disorders, genetic causes of infertility, hormonal imbalances, and immunological aspects of infertility.

The majority of infertility causes will fall into one or more of the following three categories:

  • Male Factor Infertility: Sperm production and sperm quality
  • Ovulation and Hormonal Production: Egg production, egg quality, and preparation of the uterine lining for implantation
  • Passage: The joining of sperm and egg in the Fallopian tubes and transport of the fertilized egg to the uterus


Female Age and Fertility:

Impact of Female Age


The loss of female fertility is due to the loss of high-quality eggs. The receptiveness of the uterus is not decreased (Donor Egg IVF remains a valuable treatment). This loss of fertility magnifies the impact of any other infertility factors present.

IVF Diet and Lifestyle:

Your physical condition could make an enormous difference between successfully achieving a birth and going through years of frustration. Optimizing your fertility potential can have a considerable impact on the probability of a successful outcome.

Please use the following links for information about reproductive treatments at Bay IVF and to request a consultation.



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