The question of whether--and when--to seek a medical opinion on your fertility can be fraught. The ability to conceive a baby when they’re ready is something many people take for granted. After years or even decades of carefully planning and avoiding pregnancy until the time was right, getting pregnant seems as if it should be “the most natural thing in the world.” When things don’t happen on schedule it can be a shock. At the same time, when you confide your worries to friends and family, you’re often advised to just relax, be patient, and to stop stressing out about it.

So when is a string of negative pregnancy tests just a matter of timing and the natural variation of the human body and when is it something that should be checked out by a fertility specialist? Here’s how to know when it’s time to see a fertility doctor.

How long have you been trying to conceive?

The most basic way to decide when to see a doctor is based on the woman’s age and the amount of time you’ve been actively trying to get pregnant. Trying here is simply defined as having regular intercourse without birth control. Generally, fertility experts recommend that you come in for an evaluation if:

• You are under 35 with regular cycles and haven’t become pregnant after 1 year
• You are 35 to 39 with regular cycles and haven’t become pregnant after 6 months
• You are 40 or over with regular cycles and haven’t become pregnant after 3 months

These guidelines are informed by statistics. An average woman in her 30s has a 15% to 20% chance of getting pregnant in an average month. After 4 or 5 months have passed, around 60% of women will have gotten pregnant, and the pregnancy rates begin to fall each month after that, down to a tiny 1% or 2% per month after a year has passed. As women get older, their fertility begins to decline more quickly, which is why time is of the essence and you should make the call earlier once you’ve passed the cutoff age of 35.

What is your medical history?

The time-based guidelines assume that you are in good health, with no history of reproductive issues or unusual symptoms. However, if you have reason to suspect that might be a problem, it’s a good idea to come in as early as possible: you don’t need to wait six to twelve months before seeking help. There are many reasons you might want to seek an early evaluation.

• Your periods are absent, irregular or particularly difficult. If you aren’t getting a period at all, chances are that you are not ovulating, either. Irregular periods can indicate a problem with your ovaries such as Polycystic Ovarian Syndrome (PCOS) which could mean that you are not ovulating regularly. Extremely painful, long, frequent or irregular periods can also be a sign of endometriosis, a condition where tissue from the uterine lining grows outside of the uterus. Endometriosis can cause fertility problems in many ways, such as creating a blockage in the fallopian tubes.

• You have had abdominal or pelvic surgery. In rare cases, surgeries such as an appendectomy can cause scar tissue to grow around your reproductive organs, damaging them or creating blockages. If you have had surgery to remove ovarian cysts or fibroids from your uterus, it’s a good idea to talk to a fertility expert when you decide to start trying for a baby.

• You have had an STI or Pelvic Inflammatory Disease (PID). An untreated sexually transmitted infection can have a serious impact on your fertility, even if you had no symptoms at the time. Pelvic Inflammatory Disease can also cause scarring or long-term inflammation in the reproductive tract.

• You have a history of miscarriages. Miscarriage is very common, and it can be a confusing issue: you may feel that because you have successfully conceived, you don’t “qualify” as infertile. However, going through two more more miscarriages can be a sign that there’s something going on that is making it hard for your body to sustain a pregnancy, and it’s a reason to consult with your doctor.

• You have or suspect a history of thyroid problems. Thyroid conditions can play havoc with your hormones, which in turn can interfere with your fertility. If you have a thyroid condition that is being monitored and managed with medication, it should be enough to avoid this issue, but it’s still worth checking with your doctor. If you think that you might be experiencing symptoms of an irregular thyroid, it’s something to check out immediately: a simple blood test can give you some answers.

• You have already had one or more children but are having trouble conceiving again. Secondary infertility can be tricky. Because you’ve already become pregnant successfully on your own, you don’t expect to struggle when you’re ready to add another baby to your family. In the time since your last baby, however, age-related infertility or a new condition may have developed.

How is your male partner’s health?

Up to one-third of couples struggling to conceive are dealing with some degree of male-factor infertility. Men don’t tend to have as many obvious signs and symptoms of reproductive problems as women. Most male-factor infertility is related to issues with the sperm, which can usually only be determined by conducting a sperm analysis in a lab. However, there are a few conditions which warrant getting in to see a specialist earlier rather than later:

• Issues with erectile dysfunction or ejaculation. For obvious reasons, a problem achieving or keeping an erection, or unusual or absent ejaculate can make it very difficult to conceive and should be addressed with a doctor as soon as possible.

• A lump or swelling in the testicles. Any irregularity in the testicles should be examined for general health reasons, but in the context of fertility it could indicate a varicocele, which is a type of varicose vein. Varicoceles are not uncommon, but they can impact sperm production. Varicoceles can be treated, though the scientific jury is still out of how effective the treatment is for fertility. In any case, if a varicocele is causing a low sperm count, there are options such as IVF or ICSI which can be highly effective.

• A history of STI. Untreated STIs, current or past, can also impact male fertility, causing inflammation or scarring which can block sperm.

• A history of infections such as mumps. Mumps are not as common as they once were, thanks to the wonders of vaccination, but men who have contracted mumps after puberty are at risk of a lowered sperm count

• A history of injury or surgery to the groin or genitals. Injuries or common surgeries such as hernia repairs could leave scar tissue behind and make it more difficult to conceive.

When it comes to your fertility, a proactive approach is always best. The sooner you start asking questions, the sooner you can begin to find some answers, and the higher your chances of successful treatment. You know your body better than anyone, so trust your gut. If you’re worried, don’t wait. A simple consultation with a fertility expert can set your mind at ease or set you on the path to a solution.