Secondary Infertility: Why Getting Pregnant Again Isn't Guaranteed

You already have a child. So when you can't get pregnant again, it's easy to feel like you don't have the right to complain. Like the grief doesn't count because you already "got your baby."

That's wrong, and it's not just an emotional take. It's medically wrong too. Secondary infertility, meaning you can't conceive after 12 months of trying if under 35 years old, or 6 months if 35 years or older, despite having carried a pregnancy before, is extremely common. You are not the exception.

As a fertility specialist who sees this and diagnoses it often, here is what’s happening in my mind regarding the work-up to determine cause followed by treatment.

Why "I got pregnant before" doesn't mean "I'll get pregnant again"

A lot changes between pregnancies. Your body isn't frozen in time from the day you delivered.

The major categories that cause secondary infertility:

• Ovulatory dysfunction. This is the biggest one, responsible for roughly a quarter of all infertility diagnoses. PCOS, thyroid disease, high prolactin, and weight changes since your last pregnancy can all interfere with ovulation.
• Tubal disease. Pelvic infections, endometriosis, or scar tissue from a prior surgery can block tubes that used to be patent and functional.
• Uterine factors. Fibroids, polyps, and scarring inside the uterus (called Asherman syndrome) after prior uterine procedures or a cesarean delivery are some of the things to consider.
• Male factor. This accounts for about half of all infertility cases, and semen quality can change over time. "He already has kids" is not a reason to skip his workup.
• Unexplained. About 15% of couples get a full workup and still don't get a clear answer. Unexplained infertility is not the absence of pathology, but rather the inability to identify the cause after extensive workup.
• Lifestyle. Weight, smoking, and alcohol use can all shift in the years between pregnancies, and all of them affect fertility.

The factor nobody wants to say out loud: age

I'm going to say the thing that's uncomfortable to hear. Age is usually the single biggest factor in secondary infertility, and unfortunately a lot of women don’t plan for future siblings based around age. Don’t feel bad about this because a lot of female physicians also make this mistake.

Fertility peaks in your 20s and early 30s. But by 40, your odds of conceiving in any given cycle are roughly half of what they were at your peak (20-25% depending on the cited study vs 8-10%). The data is stark: childlessness rates climb from 6% for women who start trying at 20-24, to 30% at 35-39, to 64% at 40-44. Miscarriage risk more than doubles between your early 30s and late 30s, and quadruples again after 40.

Understanding this can help with acceptance and possibly even with planning your future family based on your age and number of desired children.

The surprising cause for many cases of secondary infertility: your C-section

This always shocks my patients when the culprit is poor healing at the C-section scar or development of scar tissue. While C-sections are generally very safe, they are not risk free. As someone who has had a C-section, i would do it all over again for the safety of mom and baby, but it’s difficult not to ignore the very small risk that can lead to future fertility problems.

A meta-analysis of nearly 600,000 women found that a prior cesarean delivery is linked to a 9% lower chance of a subsequent pregnancy and an 11% lower birth rate compared to vaginal delivery. A Norwegian study of over 42,000 women found infertility rates of 9.9% after cesarean versus 7.3% after vaginal birth.

Now, to be fair: this isn't necessarily the surgery causing the problem on its own. Women who already have a harder time conceiving are also more likely to end up with a cesarean in the first place. So some of this link runs in both directions and is what we call in medicine a confounding variable. But part of it is still mechanical.

Isthmocele: the scar defect nobody checks for

An isthmocele is a small pocket or indentation in the uterine wall where a cesarean scar didn't heal properly. It's showing up more and more as cesarean rates rise worldwide.

If you've had postmenstrual spotting, unusual pelvic pain, or unexplained secondary infertility since a C-section, this should be evaluated by ultrasound (keep in mind routine 2D ultrasounds can miss this and therefore a saline infusion sonogram is a superior test). Among women with a symptomatic isthmocele, about 43% report secondary infertility as their main complaint. Across studies, anywhere from 27% to 75% of women with these scar defects experience secondary infertility.

Why would a scar affect fertility? A couple theories:

1. Fluid and blood pool in the defect, creating a hostile environment for sperm and embryos
2. Pain and abnormal bleeding can simply reduce how often you're able to have sex

If you're going through IVF and have an isthmocele, your live birth rate is significantly lower than someone with a prior C-section but no defect. The good news: this is often fixable. A hysteroscopic repair, done when there's enough remaining muscle tissue, has a live birth rate around 63% afterward, with some studies showing pregnancy rates as high as 71%.

The diagnostic workup as previously mentioned should include: a transvaginal ultrasound, ideally combined with a saline infusion to see the uterine cavity clearly. If you've had a C-section and you're struggling to conceive again, ask specifically about this. It's not part of every standard workup if you’re not seeing a reproductive endocrinologist

What a real secondary infertility workup should include

Everything from a standard fertility workup still applies: checking ovulation, a semen analysis, tubal testing, ovarian reserve testing. But if you've been pregnant before, there are a few extra questions your doctor should be asking:

• How did you deliver? If it was a C-section, is there an isthmocele?
• Did you have any complications after delivery, like an infection or a D&C, that could have caused scarring?
• Has your weight changed? Are you on new medications? Are you breastfeeding?
• If you're 35 or older, have you had your ovarian reserve checked (AMH, FSH, antral follicle count)?
• Could you have new-onset endometriosis or fibroids that weren't there before?
• Has your partner had a semen analysis, even if he already has kids?

Where treatment goes from here

Treatment follows the cause, same as it would for anyone. But two things matter more here than in a typical first-time fertility workup.

First, age drives the timeline. IVF success drops sharply after 40, and live birth rates per transfer fall to around 11% for women over 43. That doesn't mean don't try. It means don't waste months on low-yield approaches when time is the one thing you can't get back.

Second, if an isthmocele is the issue, surgical repair may need to happen before, or instead of, jumping straight to IVF.

The TLDR

Secondary infertility is common, and it deserves to be taken seriously. Having a child before does not guarantee you'll have one again. Age is the biggest factor in most cases, and treatment strategy should be based on age and future family building goals. And if you've had a C-section, your cesarean scar is worth investigating.

You're allowed to grieve this, even with a child already in the next room. The confusion, the frustration, the feeling that nobody understands why this is so hard the second time around, all of that is valid. Get the full workup. Ask the specific questions. And don't let anyone, including yourself, tell you this doesn't count.

If you wish to learn more in greater detail be sure to check out my YouTube episode on secondary infertility https://youtu.be/LCvbtGnKZas?si=Tq_ASBE32nYZp4Im