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Why You May Not Be Getting Pregnant, Despite Having Sex in Your Fertile Window

Why You May Not Be Getting Pregnant, Despite Having Sex in Your Fertile Window

Dr. Wade Webster, MD | April 19, 2019 | Getting Pregnant
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When trying to conceive, timing sex correctly is critical — your fertile window lends you the highest chance of conceiving. In fact, major studies show that you are approximately 30% likely to get pregnant if you have intercourse 0-1 days before ovulation. While 80% of couples conceive within 6 months when correctly timing intercourse , many people have difficulty getting pregnant after 12 months of trying. If you’ve been having sex in your fertile window but haven’t conceived yet, you may be wondering why. While infertility may be related to symptoms such as irregular periods, many causes of infertility are present without clear indicators. Below are some of the most common causes of infertility.Looking for a new way to identify your fertile window? Check out the Priya Personal Fertility System!


Missing the fertile window

If you are relying on apps or waiting to have intercourse when you get an LH-surge, you may actually be missing your fertile window. Apps can only estimate when you ovulate based on historical data, like start and end dates of prior periods, but this cannot account for what is actually happening inside your body on any given day. Even for those with cycles that are considered regular, some variation is expected from cycle to cycle, and ovulation may occur sooner or later than an app or ovulation calculator predicts.

Although LH- sticks to predict ovulation are found to be highly accurate, it is possible to miss the fertile window for a couple of reasons. One is that the fertile window is 3-5 days prior to ovulation and the day of ovulation. The LH test kits can only indicate at most half of the fertile window; the days with the highest probability of conception often occur prior to a detectable LH surge.

Second, the fertile window may be missed with LH sticks because an LH surge may last less than 10 hours, so once-per-day testing may not catch the surge. False increases of LH may happen before the true surge, especially with certain conditions like PCOS.

Looking for a new way to identify your fertile window? Check out the Priya Personal Fertility System!

Absence of ovulation

No matter when or how frequently you have sex, conception requires ovulation. Anovulation is when the ovaries do not release an egg during the menstrual cycle, and it can be caused by many conditions. Some causes of anovulation include PCOS (polycystic ovarian syndrome), obesity, low body weight, hyperprolactinemia (high blood levels of the hormone prolactin), and high stress levels.

A reliable and inexpensive way to confirm ovulation after it has occurred (note that this method does not predict ovulation) is by tracking basal body temperature (BBT). BBT is your body’s temperature at rest, which means the temperature needs to be measured after at least 4 consecutive, solid hours of sleep and before any other activity happens -- before going to the bathroom, getting dressed, etc. In a regular menstrual cycle, BBT will be in a bi-phasic pattern; pre-ovulation temperatures will be lower, then the day after ovulation, BBT will increase by 3/10ths of a degree Fahrenheit (often referred to as the temperature shift) and remain elevated until menstruation, usually about 12-15 days, which are known as the luteal phase.

One of the main signs of anovulation is having irregular cycles. If you have irregular periods, it is best to talk to your doctor about your fertility health, regardless of how long you have been trying to conceive.

Fertility and age

Many different variables can affect fertility, some of which are under debate even among experts, but one factor is age. While couples may successfully achieve healthy pregnancies late into their thirties and forties, egg/sperm quality and count decrease for men and women with age. Women begin to see a drop in fertility at the age of 35, and men see a decline at 40 years of age. A study that investigated the time to pregnancy (TTP) of different age groups found that 77.5% of women under the age of 25 were able to become pregnant within 6 months, compared to 58.4% of those over 35 years old. Similarly, 76.8% of men below the age of 25 were able to impregnate their female partners within 6 months, compared to 52.9% of men over 45 years of age. Click here to read more about age and fertility.


Endometriosis is a condition where the endometrium (tissue lining the uterus) grows outside of the uterus. Among other organs, this endometrial tissue may grow on your ovaries and fallopian tubes which could cause scarring that influences infertility. This condition is characterized by irregular periods, excessive bleeding, and pain with intercourse. However, among those who have this condition, 20-25% of them do not experience symptoms and only discover their endometriosis after visiting their doctor for infertility. Of the women who are affected by endometriosis, 30-50% experience infertility. Unfortunately, at this time, endometriosis can only be diagnosed with laparoscopic surgery. Because of this, endometriosis diagnoses often come after years of experiencing symptoms and chronic pain. If you suspect you may have endometriosis, it is best to bring these concerns up with your doctor.

Looking for a new way to identify your fertile window? Check out the Priya Personal Fertility System!

Male infertility

An often-ignored factor in trying to conceive is male fertility. Men typically present silently with infertility — in other words, they have no outward symptoms — so determining your male partner’s fertility status is difficult without a semen analysis. In about 30% of couples who have difficulty getting pregnant with unprotected sex, the primary fertility concern lies with the male. While the cause of male infertility is mostly unknown, major influencing factors include genetics and the decline of sperm quality with age. Sperm may have an odd shape, show underdevelopment, or have limited motility. When consulting your doctor about infertility concerns, it is important that both male and female partners get tested.

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Closing remarks

Struggling to get pregnant or being diagnosed with infertility may feel overwhelming and lonely, but a wealth of resources is available to help you through this process. You are not alone. The most important step to schedule an appointment with your doctor to discuss your concerns and get the help you need. As with any health issue, knowledge is power, and keeping track of symptoms is essential. The causes for infertility may not always seem obvious, and this list certainly doesn’t contain every possibility, however, the sooner you explore your fertility health, the sooner you can set off on the path to conception.

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References +

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Wilcox et al. (1995). American Pharmacists Assoc NEJM 333(23):1517-1521 5.; Obstet Gynecol. 2002 Dec;100(6):1333-41. Timing intercourse to achieve pregnancy: current evidence. Stanford JB1, White GL, Hatasaka H.


Hsiu-Wei Su and team. Bioeng Transl Med. 2017 Sep; 2(3): 238–246.Published online 2017 May 16. doi: 10.1002/btm2.10058


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