Why Am I Struggling to Get Pregnant With My Second Child? Secondary Infertility Explained

When the first pregnancy happens easily and the second one doesn’t, it can feel like something has gone quietly wrong. For most patients, what has changed is one of a small set of medical, biological, or life factors. This guide walks through the most common ones.

The most important factor is almost always time

For most patients, the single largest change between the first pregnancy and the second is age. Ovarian reserve — the number and quality of eggs remaining — declines steadily after age 30 and more steeply after age 35.[¹]

Even a gap of two to three years between attempts meaningfully changes the statistical odds. A patient who conceived easily at 31 may find the same biology no longer cooperates at 35. The calendar matters more than most people expect it to.

If you are over 35 and have been trying for more than six months, the time variable alone is worth investigating.

Hormones may not have fully returned to baseline

The hormonal landscape after a pregnancy is not identical to before it.

Breastfeeding: suppresses ovulation in many women — sometimes for months after weaning begins. Cycles often return on a delay, and the first several cycles after weaning may be irregular before regular ovulation resumes.

Postpartum thyroid dysfunction: affects roughly 5 to 10 percent of women within the first year after delivery, and can persist longer.[²] Thyroid disease is one of the most easily corrected hormonal contributors to secondary infertility.

Prolactin: elevation, sometimes caused by ongoing low-level milk production or medications, can suppress ovulation.

A complete hormonal workup is part of a standard secondary infertility evaluation.

Conditions that weren't there before — or weren't symptomatic

Several gynaecological conditions can develop or worsen in the years between pregnancies:

Polyendocrine metabolic ovarian syndrome (PMOS, formerly known as PCOS): can become more symptomatic after a previous pregnancy, particularly if weight has increased since.

Endometriosis: may have been present without symptoms before the first pregnancy and can become more clinically apparent over time. Endometriosis affects egg quality, fallopian tubes, and implantation.

Uterine fibroids: can grow in the years after a first pregnancy and may interfere with implantation or carrying a second pregnancy.

Adenomyosis: endometrial tissue in the uterine wall — is increasingly recognised as a contributor to secondary infertility and miscarriage.

‍Caesarean scar defect: a niche or pocket in the previous Caesarean scar — is a less-discussed contributor that can cause persistent post-menstrual bleeding, fluid in the uterine cavity, and difficulty conceiving. It is found more often than it is asked about.[³]

If any of these conditions are suspected, they can usually be identified through transvaginal ultrasound, saline sonohysterogram, or hysteroscopy.

Male factor — often unchecked the second time

Sperm quality also changes over time. About 30 percent of secondary infertility cases involve a male factor that has emerged or worsened since the first pregnancy.[⁴] Common contributors include:

• Aging (sperm parameters decline after the late thirties)
• Weight gain
• New medications (including some commonly prescribed for depression, blood pressure, hair loss, and chronic pain)
• Heat exposure (regular hot tub or sauna use)
• Undiagnosed varicocele

A semen analysis is recommended in every secondary infertility evaluation, even if the male partner had a normal result before the first pregnancy. Sperm parameters can change meaningfully in three to five years.

Life with a small child changes the body in ways that matter

Several factors that are universal to parenting a young child can affect fertility:

Sleep: is often interrupted for months or years. Sleep loss disrupts hormone regulation in both partners.

Weight changes: both gain and significant loss — affect ovulation and sperm production.

Stress and cortisol elevation:  affect ovulation in some patients.

‍Frequency of intercourse: drops in many couples after the first child, simply because life is busier. Tracking ovulation can help focus attempts.

None of these alone explains most secondary infertility, but they are often part of the picture and are usually modifiable.

When to take it seriously

The recommended timelines for evaluation are:

• Under 35: after 12 months of trying without success
• 35 to 39: after 6 months
• 40 and older: without delay

In Ontario, you do not need a family physician's referral to book a fertility consultation, and initial consultations are typically covered by OHIP.

If you have known concerns — irregular cycles, a previous Caesarean delivery, painful periods, a history of pregnancy loss, or PMOS — earlier evaluation is appropriate.

Frequently asked questions

Can secondary infertility be temporary?

Sometimes, yes. If the cause is a hormonal imbalance, weight change, breastfeeding-related anovulation, or a treatable thyroid condition, fertility can return after the underlying issue is addressed.

Should I get tested even if my first pregnancy was easy?

Yes, if you meet the timelines above. A previous easy pregnancy is not a guarantee that fertility today is unchanged.

Does my partner need to be tested again?

Yes. Approximately one in three secondary infertility cases involves a male factor that wasn't present at the first pregnancy. A new semen analysis is part of a complete evaluation.

Will the cause always be identified?

No. Approximately 10 to 15 percent of evaluations return as unexplained.[⁵] A working diagnosis of unexplained secondary infertility still allows for effective treatment.

References

1. Liu K, Case A. *Advanced reproductive age and fertility: SOGC clinical practice guideline.* J Obstet Gynaecol Can. 2017.

2. Stagnaro-Green A. *Approach to the patient with postpartum thyroiditis.* J Clin Endocrinol Metab. 2012;97(2):334–342.

3. Tower AM, Frishman GN. *Cesarean scar defects: an underrecognized cause of abnormal uterine bleeding and other gynecologic complications.* J Minim Invasive Gynecol. 2013;20(5):562–572.

4. Practice Committee of the American Society for Reproductive Medicine. *Diagnostic evaluation of the infertile male: a committee opinion.* Fertil Steril. 2015.

5. Practice Committee of the American Society for Reproductive Medicine. *Effectiveness and treatment for unexplained infertility.* Fertil Steril. 2020.

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‍*This article is for educational purposes and does not replace individual medical advice.*