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Ovulation To Conception & Fertilization Of The Ovum

Ovulation To Conception & Fertilization Of The Ovum: Part 2

In the first article of this five-part series, we took an in-depth look at the first two phases of the menstrual cycle- the Menstrual phase and the follicular phase. We saw how your body prepares itself for ovulation during these stages of the cycle. Estrogen. LH and FSH play a crucial role in developing the ovarian follicle and building up the endometrium of the uterus. The egg in the follicle also matures under the influence of these hormones.

In part two, we will take a closer look at what happens during ovulation and during the latter half of your menstrual cycle, called the Luteal phase.

Ovulation - sperm meets egg
Image courtesy of conceive health

Ovulation

The release of a mature egg from one of the ovarian follicles is called ovulation. You are at your peak fertility during this time of the month. If you are trying to conceive, it is the best time to have sex. Your fertile window is 4-5 days before the actual ovulation and the day of ovulation. Significant physiological changes are happening during this time, and we will take a look at all of them in the following sections.

The level of estrogen is high during both the follicular and ovulatory phases. The higher amount of estrogen ensures the proper building up of the endometrial lining of the uterus. The elevated estrogen levels also provide that the pituitary releases LH at the right time during the menstrual cycle.

The cervical secretions are also stimulated under the influence of estrogen. As you approach your ovulation date, the volume of cervical mucus increases significantly, and the consistency and appearance also change.

The changes in the cervical mucus happen as the body is trying to make the environment conducive for the sperm. When you approach the ovulation, the cervical mucus becomes clear and stretchy and attains the consistency of an uncooked egg-white. During this time, the mucus is most conducive for sperm motility. It protects the sperm from the harsh environment of the female reproductive tract as well. Hence, a fertile and conducive cervical mucus can increase the chance of you conceiving.

Vaginal discharge colours: what do they mean?
Image courtesy of The Bright Girl Guide by Demi Spaccavento.

The consistency, appearance, and volume of cervical mucus can be a great sign to predict fertile window and ovulation. As your cycle progresses from the menstrual phase to the ovulatory stage, you might see a distinct change in the cervical mucus. The volume of the mucus is less in the menstrual phase of the cycle but increases through the ovulatory phase and is maximum just before and after ovulation. The consistency and appearance also change. While the mucus might be white or yellow at the beginning of your cycle, it becomes clear and slippery near the ovulation. The ‘egg-white‘ cervical mucus is a clear indicator of impending ovulation, and it is the most conducive to the sperm.

So, we’re on day 14 of the cycle. In the first weeks of the period, estrogen is dominant, but LH suddenly increases in concentration – and in a big way! You will undergo what is known as the ‘LH surge’ in the middle of the cycle. As previously said, LH weakens the wall of the ovarian follicle. The egg escapes the follicle and heads into the fallopian tube. The inner surface of the fallopian tubes is lined by microscopic hair-like structures called the cilia that guide the egg down the fallopian tubes. Ovulation can be detected by an ovulation prediction kit (OPK). Using an accurate OPK from Fertility2Family, you can pinpoint your ovulation and fertility window with great accuracy. A positive test result indicates that you are going to ovulate within the next 12-36 hours.

Ovulation occurs shortly after the LH surge, typically around midcycle. The egg is released and has a 24-hour life span, so having sex right time increases your chances of getting pregnant faster. Illness, insomnia, flight, stress, and hormonal imbalances may cause ovulation to be delayed or interrupted. Most women ovulate simultaneously per month (depending on cycle length), but you can ovulate at different times during your cycle if your cycle is erratic. There are only a few physical signs and symptoms of ovulation. Midcycle pains, also known as mittelschmerz, are cramp-like pains on one side of the abdomen that can affect some but not all women. An increase in sexual desire may be a fertility predictor and makes sense, as you are at your peak fertility at this time, and if you have sexual intercourse, there is a greater chance that you will conceive.

Ovulation spotting can also be seen in some women. It is a form of very light bleeding resulting from the rupture of an ovarian follicle. However, not all women experience such ovulation spotting. Not many studies are available on this topic, and hence, ovulation spotting shouldn’t be considered a sign of ovulation.

In some women, ovulation may cause tenderness in the breast as well. To make the matter a bit more confusing, breast tenderness and nipple sensitivity can be early signs of pregnancy. Hence, how your breasts feel might not be an accurate indicator of your ovulation and fertility window. BBT is one of the better indicators of ovulation, and if you chart your BBT throughout your cycle, it can give some accurate predictions regarding your fertility window. You can order your own BBT thermometer from Fertility2Family.com.

The levels of estrogen after ovulation drop, and the LH levels drop dramatically. During the post-ovulation phase of your cycle, progesterone is the dominant hormone. Progesterone is secreted by the left-over mass of the ovarian follicle called corpus luteum. Progesterone warms the body up and makes it ready for pregnancy. If you have been keeping records of your BBT, this is where you will see an increase in your basal body temperature.

Week 3: Conception and implantation

After ovulation, the egg is swept inside the fallopian tube by the finger-like projections at the mouth of the tube called fimbriae. The egg then moves along the fallopian tube towards the uterus with the help of microscopic hair-like structures called cilia that line them on the inside. If you plan your sexual intercourse correctly, about 300-400 million sperms might be waiting for the egg to arrive. Most of the sperms, however, will be destroyed and will never get a chance to see the egg, let alone fertilize it. Some sperms might move in the wrong direction, and some might be destroyed by the immune cells present in your reproductive tract. Of these millions of sperms ejaculated in the vagina, only a few hundred healthiest ones will survive and reach the egg. Using sperm-friendly lubrication can increase your chances of more sperm reaching the egg.

Fertilization

The journey of the sperm culminates in fertilization. Once the remaining sperms meet the egg in the lower quadrant of the fallopian tube called the ampulla, the race to fertilize it begins. The sperm cells start circling the ovum finding a way through the protective layer called the Zona Pellucida. Specific proteins on the sperm and the zona pellucida (called receptors) need to contact the sperm to enter the ovum. Once a single sperm cell establishes this contact and completes the receptor interaction, it gains entry into the ovum. After its entrance, a signalling mechanism immediately blocks the access of other sperm cells into the ovum. The nucleus of the sperm then fuses with the nucleus of the ovum marking the completion of fertilization, and just like that, the ovum is now a zygote. The zygote continues its journey down the fallopian tubes to the uterus and starts to divide en route.

Implantation

Fertilization and conception are not synonymous. Your pregnancy does not start till the developing embryo implants itself in the uterine wall. The zygote formed after fertilization is still free-floating before implantation and continues to divide and differentiate. The differentiated mass of cells is called a trophoblast that contains an amniotic sac, a placenta, and an umbilical cord. For a successful pregnancy, the embryo must embed itself into the thick uterine lining called the endometrium. Implantation takes place after a few days to a week after ovulation. Once the embryo is implanted successfully, and a connection between the mother and fetus is established, you are officially pregnant!

Once the implantation is successful, and the placenta is developed, it takes over hormone synthesis from the corpus luteum. We will talk about the sequence of events leading to the luteal phase in the third part of this series.


Fertility2Family Five Part series 

Part One: Ovulation To Early Pregnancy A Week By Week Cycle
Part Two: Ovulation to Conception and Fertilization of the Ovum
Part Three: Implantation, Progesterone, hCG Tests, & the Luteal Phase
Part Four: Pregnancy Symptoms, Morning Sickness & Fatigue
Part Five: First Trimester Pregnancy Signs