Secondary Infertility: Why Conceiving a Second Child Can Be Challenging

Many couples assume that if they've successfully conceived once, they'll have little trouble when planning for their next child. However, fertility specialists are seeing a rising number of parents seeking medical assistance for conceiving their second child—a condition known as secondary infertility. We learn more from Dr Roland Chieng, our medical director.

The Timing Challenge: Conceiving in Your Thirties

Most couples try for their second child when they're in their thirties. This timing makes sense, as the average age of first-time parents today has increased in recent years due to various socio-economic factors, including couples marrying later. By the time many parents consider a second child, they're well into their thirties.

According to Dr Chieng, he is seeing more secondary fertility cases at his clinic.

“Most of the cases are related to the age of women at first pregnancy. Commonly the thoughts of a second pregnancy starts 2-5 years later after the first birth. Age does affect the remaining number of eggs and their quality.”

“The condition is known as secondary infertility and it refers to the inability to conceive after previously achieving pregnancy or pregnancies without medical intervention,” he explains.

Symptoms similar to primary fertility

The symptoms are often similar to those of primary infertility, such as irregular or absent periods and changes in menstrual flow. Other usual signs are struggling to get pregnant despite trying for 6 to 12 months (depending on age) and pelvic pain, which could be due to fibroids or endometriosis.

There is also the male factor to consider. In men, symptoms such as erectile dysfunction, reduced sperm count, low libido, or testicular pain/swelling can contribute to secondary infertility.

Can you experience unexplained infertility after a natural birth?

When we thought we had a first child naturally, unexplained infertility is not on the cards. According to Dr Chieng, that is not the case.

“Unexplained infertility refers to situations when initial investigations and tests on sperm, ovulation, pelvic factors, all showing normal result. This could still happen with secondary infertility.”

A common myth that single child runs in the family. According to Dr Chieng, that’s not the case. “Secondary infertility is not directly hereditary in the same way that genetic conditions are inherited.”

5 Top Reasons Why Conceiving a Second Time Can Be More Difficult

The gap of just a few years between first and second pregnancy attempts can significantly affect fertility in both partners. Here are key factors to consider:

1. Diminishing Egg Supply from Birth

“Age ranks as a key reason for secondary infertility. After the age of 35, fertility declines compared to earlier years. Unlike other cells in the body, women do not produce new eggs throughout their lifetime—they are born with a finite number of eggs,” Dr Chieng says.

This supply naturally diminishes over time:

• At birth: approximately 1,000,000 eggs
• By puberty: roughly 500,000 eggs
• In the twenties: about 200,000 eggs

Fertility begins to decline around age 32[1], gradually at first, then more rapidly in the mid-to-late thirties, and steeply in the forties. Since the rate of decline varies from woman to woman, the only reliable way to assess fertility is through testing.

2. Egg Quality Declines with Age

As women age, their eggs are more likely to contain chromosomal abnormalities[2]:

• In their early 30s, about 10–25% of eggs
• At age 40+: more than 50% of eggs are affected.

These statistics explain why conception becomes more challenging and pregnancy complications increase with maternal age.

Does natural birth cause decline in egg reserves?

Dr Chieng says, “Pregnancies does not affect the quantity of eggs. The reserves typically stay stable till after age 35.”

3. Lifestyle Demands

By their mid-to-late thirties, couples often face different pressures than they did when younger.

“As commitments and responsibilities increase—such as career demands and family obligations—couples may engage in sexual activity less frequently. For those with borderline subfertility, where conception is possible but may take longer, reduced intercourse frequency can further decrease the chances of pregnancy, as timing plays a crucial role in fertility,” Dr Chieng explains.

Plus, parenting a young child does affect conception efforts. This practical factor is often overlooked: caring for a toddler is physically and emotionally demanding. Parents of young children frequently have less energy for intimacy and in cases of co-sleeping arrangements, conception opportunities is reduced.

4. Change in Ovulatory Condition

“Change in physical changes such as increase in body weight can cause change in ovulation,” Dr Chieng says.

Weight changes can affect ovulation, making it harder to get pregnant. Being too thin may stop ovulation completely while being overweight can lead to hormone imbalances and irregular periods. An unhealthy diet without enough essential nutrients like vitamin D, iron, and omega-3 can also affect hormone levels and fertility. Too much intense exercise[3], especially with low body fat, can also stop ovulation, reducing the chances of conception.

5. Gynecological Issues Become More Common

With age, women may develop various conditions that can impair fertility:

• Fibroids: These growths develop in and around the womb and can obstruct implantation, especially if they protrude into the uterus (submucosal fibroids). Multiple large fibroids may also increase the risk of premature labor.
• Polyps: These small, raisin or grape-sized growths can prevent sperm from reaching the fallopian tubes or block embryo implantation.
• Cysts: It forms when uterine lining tissue grows within the ovaries. They can impact egg quality and diminish egg reserves over time.

Final Thoughts

Secondary infertility can be an unexpected and emotional challenge for many couples who assumed that conceiving again would be as straightforward as their first pregnancy. As fertility naturally declines with age, factors such as egg quality, lifestyle changes, and underlying gynecological conditions can contribute to difficulties in conception. However, early assessment and intervention can improve the chances of success.

If you are experiencing difficulties conceiving a second child, consulting a fertility specialist can help identify potential issues and explore suitable treatment options. Understanding the factors affecting you helps make informed decisions and take proactive steps toward growing your family.

[1] https://www.medicalnewstoday.com/articles/how-many-eggs-does-a-woman-have

[2] Thomas C, Cavazza T, Schuh M. Aneuploidy in human eggs: contributions of the meiotic spindle. Biochem Soc Trans. 2021 Feb 26;49(1):107-118. doi: 10.1042/BST20200043. PMID: 33449109; PMCID: PMC7925012. https://pmc.ncbi.nlm.nih.gov/articles/PMC7925012/

[3] Mussawar M, Balsom AA, Totosy de Zepetnek JO, Gordon JL. The effect of physical activity on fertility: a mini-review. F S Rep. 2023 Apr 14;4(2):150-158. doi: 10.1016/j.xfre.2023.04.005. PMID: 37398617; PMCID: PMC10310950. https://pmc.ncbi.nlm.nih.gov/articles/PMC10310950/