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what factors affect fertility?

For most couples, the instinct to start a family is the most natural thing in the world. So, when couples trying for a child run into problems, they can become anxious and even confused over what their next course of action should be.

It is important for each couple to understand that their difficulty in conceiving or in achieving live birth is a result of a unique set of circumstances. Therefore, the chances of fertility treatment success varies widely amongst even similar demographics (such as age and gender). The success of assisted reproductive treatment depends on many factors.

1. The age of the woman

The single most important factor that affects a woman’s fertility is her age (Figure 1). This is primarily due to the fact that women are born with all the eggs you’ll ever have in your lifetime. As women age, the quality as well as the quantity of eggs decline. Although menopause does not occur in women until the early 50s, for most women, fertility starts to decline after the age of 35. From about 40 years of age, the drop in fertility is profound. It is therefore important that women who are reaching 35 and have not been able to become pregnant seek medical attention soon. This becomes urgent for women who are nearing 40 years of age.

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2. The length of time trying to conceive

Once you decide to have a baby, it is easy to become concerned if you do not conceive within the first month of trying. But the fact is, even a normal, healthy woman (below the age of 30) who is regularly having intercourse only has a 20 to 40 percent chance of getting pregnant during any given cycle. So, what goes “wrong” the other 60 to 80 percent of the time? In most cases there is no medical reason – the cause is usually because the quality of the egg or sperm is insufficient to achieve fertilisation, or that fertilisation occurs but the embryo does not survive beyond a few days. In fact, the odds of conception are actually quite good once you look at them over the span of a year of trying, according to data from the National Center for Health Statistics in USA (Figure 2).

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3. Being Over or Under Weight

For both men and women, being overweight or underweight can adversely affect fertility. Women who have body fat levels of 10 to 15 percent over the normal fat percentage can have excessive amounts of estrogen in the body, affecting their reproductive cycle. Conversely, women with body fat levels 10 to 15 percent lower than the normal fat percentage can shut down the body’s normal reproductive process.

For men, obesity lowers the sperm count and being underweight lowers the quality of the sperm. Both lead to a lower rate of fertility.

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4. The age of the man

Although men continue to produce sperm throughout their life, it is now known that the quality of their sperm lowers as they age. Older fathers also carry a higher risk of miscarriages (the risk of miscarriages among women with male partners above the age of 45 is twice as high as those with partners under the age of 25).

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5. Hormone levels

Certain hormones, such as the gonadotropin-releasing hormone (GnRH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH), oestrogen and progesterone affect the reproductive cycle and when they are in imbalance, they can disrupt the normal process of reproduction. In cases such as PCOS (Polycystic Ovary Syndrome), elevated levels of androgens (such as testosterone) prevent a woman’s body from ovulating regularly thus leading to infertility. Hormonal imbalances in males such as low testosterone can affect sperm production and quality.

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6. Issues with reproductive organs

Damage to the reproductive organs can result in infertility in both men and women. For example, endometriosis which causes tissue that normally grows on the inside of the uterus to grow on the outside and spread to other surrounding organs may cause cysts or blockages that prevent conception. For men, disorders such as varicocele, which causes the swelling of the veins that drain the testicle, can result in reduced sperm quality.

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When should I seek medical assistance to conceive?

Do not delay seeking medical help, as your age is of crucial importance in determining fertility. The following points will help you to decide when you should seek urgent medical advice:

In the absence of any medical problems, women below the age of 30 should see a gynaecologist if they have trouble conceiving after one to two years of unprotected intercourse. However, those between 30 and 35 should seek attention after six to nine months. The urgency increases in women between 35 and 40 if they are not pregnant after six months; while women over 40 should seek medical attention after three months of unsuccessful trying. If you have been unsuccessful in conceiving or if you think you may have fertility issues, it is best that you undergo fertility screening as a couple to figure out what your fertility issues and chances of successful pregnancy are.

In most instances, your gynaecologist should be able to perform a preliminary fertility regime and treat most of the problems, if any. If you have not conceived under your doctor’s care within six to 12 months, see a fertility specialist [also called an RE (Reproductive Endocrine) specialist, who is a gynaecologist with additional experience in fertility management], who can guide you through the wide range of available treatments.

With effect from 1 January 2020, the Singapore Government has lifted the maximum age limit of 45 years for a woman to go for assisted reproductive technology (ART) treatments. The limit to the maximum number of ART treatment cycles a woman can undergo has also been removed. However, this should not be taken as a reason to delay trying as age is still an important factor to the success of ART treatments.

It is important to understand the thinking process of your doctors so a decision that is correct for you can be made. This means that YOU actively participate in your treatment and assist your RE specialist in formulating the best possible plan to becoming pregnant.


Want to find out more about the services we provide? Do you have any questions about your particular situation or are you looking to book an appointment with one of our fertility specialists?