The Difference Between Subfertility vs. Infertility

If you and your partner have been trying to conceive a baby and have not yet been able to, your fertility specialist may inform you that you, your partner, or both of you as a couple are subfertile. While dismaying at first, it shouldn't necessarily dishearten you.

Subfertility simply means that you, as a couple, are less fertile than other couples like you. It doesn't mean you won't get pregnant; it simply suggests that it may be more difficult based on the various measures used to assess your fertility.

Differentiating Between Subfertility and Infertility

Someone who is described as being subfertile still has a chance of getting pregnant on their own, although it may take longer than others. This is compared to someone who is infertile, needs medical assistance to get pregnant and is unlikely to get pregnant without help.

Another difference between the terms is that infertility means you have been trying to get pregnant for at least one year without success. Subfertility, on the other hand, simply means that it's taking longer than average to get pregnant. You may have been trying for one year, or you may have been trying longer.

Neither the term subfertile nor infertile should be confused with a person considered sterile. While an infertile person may have a very, very tiny chance of getting pregnant on their own, someone who is sterile is unable to get pregnant without medical assistance.

Here's where it can get confusing: a couple who tries for at least one year is by definition called "infertile." This is why you should see your doctor if you don't get pregnant after a year (or, after six months if you're age 35 or older.)

However, some couples who don't conceive after a year are actually subfertile. That is to say, they will conceive on their own eventually—they just need more time. They don't necessarily require fertility treatment.

How Many Couples Are Infertile? How Many Are Subfertile?

Of couples who were trying for an average of a year and a half without success, one study found that 47 percent were actually infertile—meaning they required assisted reproductive technologies to conceive and did not get pregnant on their own during the course of the study. This particular study excluded couples with a known fertility problem. The diagnosis for most of these couples would be unexplained infertility (a diagnosis of elimination.) 

The longer a couple tries to get pregnant without success, the further down their odds for natural conception drop.

According to another study, if you had 100 couples trying to conceive…

• 70 would conceive after six months
• 20 more would conceive after another six months
• 5 would conceive spontaneously within the next 36 months (three years)
• 5 of the original 100 couples would be extremely unlikely to ever conceive on their own

This study found that couples who had been trying for 48 months—or four years—had “a nearly zero chance” of conceiving without medical assistance. 

Causes and Diagnosis of Subfertility

The causes of subfertility are essentially the same as those for infertility and can vary by partner. For women, causes may include ovulation problems and age-related factors. In men, lower than average sperm count can be the issue. In some cases, the combined characteristics of the male and female partner can contribute the subfertility.

Many subfertile couples, however, will receive a diagnosis of unexplained infertility. This is a diagnosis of elimination. In other words, after basic fertility testing, everything looks fine in both the female and male partner. This doesn't mean there isn't a fertility problem—only that it isn't obvious.

Basic fertility testing can include:

• Ovarian ultrasound
• HSG (a special X-ray that evaluates the fallopian tubes and uterine shape)
• Semen analysis
• Hormone testing in the female partner (link Anti-Müllerian hormone and follicle stimulating hormone)
• Genetic testing to rule out chromosomal disorders (if there have been recurrent pregnancy losses)

Other diagnostic techniques (laparoscopic, hysteroscopic) may be used if the results of these basic tests come back unclear or if there are symptoms that warrant further exploration (like pelvic pain, for example.)

If a woman is found to have blocked fallopian tubes, or a man has an extremely low or zero sperm count, then they are infertile (or even sterile) and will require medical assistance to conceive.

Boosting Subfertility With Lifestyle Changes

The main difference between couples that are subfertile and those that are infertile is in how the condition is treated. In subfertile couples, treatment may not be so immediate or aggressive, particularly in the early stage.

Instead, your specialist may opt for lifestyle changes and recommend fertility awareness methods to boost your odds of conceive. Recommendations might include:

• Avoiding smoking which affects both male fertility and female fertility
• Exercising moderately but not excessively (which can affect sperm count and a woman's menstrual cycle)
• Monitoring your basal body temperature and cervical fluids more closely
• Adjusting the frequency of sexual intercourse
• Weight reduction as obesity can affect fertility
• Avoiding sexual lubricant that can affect sperm motility
• Avoiding overheating the testes (through hot baths, saunas, or showers)

If these interventions are unable to lead to conception, fertility treatments may be explored including fertility drugs, surgery, assisted reproductive technologies, or a combination of treatments.

Wait and Keep Trying? Or Begin Fertility Treatments?

How do you and your doctor decide whether you should keep trying on your own, or move onto fertility treatments? While you could consider fertility treatments after one year of unsuccessful trying (or after six months, if you’re age 35 or older), there are situations where you might want to wait and try for a little longer.

Fertility experts have long tried to create a formula to help doctors know when to recommend fertility treatment immediately and when to suggest lifestyle changes and trying a bit longer.

There really are no hard rules to follow. It’s a decision best made with your doctor and partner based on your particular situation.

With that said, here are some guidelines to consider.

You might want to keep trying for a little longer if...

• You are younger than 35.
• You have been trying on your own for less than two years.
• You and your partner have had basic fertility testing (blood work, semen analysis, transvaginal ultrasound, and an HSG to evaluate the fallopian tubes and uterus), and the testing has all come back normal.

For those older than 35, it’s recommended that treatment is started sooner than later. It’s equally true that older couples will naturally take a little longer to conceive on their own, due to age-related declines in fertility. However, because fertility declines quickly after age 35, waiting may mean it’s less likely for treatments to be successful.

If you’re age 35 or older, have had basic fertility testing and had everything come back normal, and want to keep trying, talk to your doctor. Depending on your particular hormone levels and situation, trying for another six months may be fine. 

A Word From Verywell

If you have been trying to get pregnant for several months without success, you are likely frustrated and maybe even worried. Does this mean you're infertile? Will you need fertility treatments to get pregnant? Not necessarily. Some couples take a little longer than average to get pregnant. Talk to your doctor if you have not conceived after one year (or after six months, if you're age 35 or older.) If all the testing comes back normal, there's a good chance you'll get pregnant on your own after another year of trying. If not—or if you want to go straight for fertility treatments—know that most subfertile couples can get pregnant with basic fertility treatments. Less than 5 percent of infertile couples will require high tech treatments like IVF.