The Impact of Age and Weight on Fertility

The Impact of Age and Weight on Fertility

couple on bike with text Dr Pooi Leng Lee

By Dr Pooi Leng Lee, Specialist at City Fertility Centre Brisbane Southside 

Two significant factors that can have an impact on your chances of conceiving are your age and your weight. In an ideal world I would encourage people to try and have babies before they are 35 years old and to have a healthy Body Mass Index (BMI). But, we all know that the world is not perfect and nor is anyone living on it! However, if it were, what should you strive for in terms of age and weight to help you conceive and what are your options if you are outside these ideals?


What is the ideal age to conceive?

Research shows that female fertility is at its optimum level until the age of 35. While women are born with their lifetime supply of eggs, these naturally begin to decline in quality and quantity from 25 and more rapidly decline from 35 years of age. The egg supply is almost non-existent by the time of menopause.

For men sperm quality also declines as age progresses but is not as rapidly as for women.

What are your options?

Start as soon as you are ready to fall pregnant if you want to optimise your chances of success. I suggest seeking the help of a specialist if you are under 35 and have been trying for 12 months without success, or if you are over 35 and have been trying for six months without success. Often early fertility interventions will be able to assist you without requiring IVF.

For the record, many people still have quick pregnancy success after the age of 35, while others it takes longer. Statistics show that by age 40, it is estimated that a female’s natural conception rate is in the range of 8-10 per cent a month and at age 43, the rate is thought to be as low as 1-3 per cent a month. Advancing age also unfortunately increases the risk of miscarriage and chromosomal (genetic) abnormalities.



What is the ideal weight range to conceive?

For women, ovulation and egg quality can be impacted by being either underweight or overweight and for men, sperm count and quality can be affected. In order to optimise your chances of success you should aim to be in the normal BMI range. The BMI ranges are:

  • Underweight: under 18.5
  • Normal weight: 18.5–24.9 (Ideal Range)
  •  Overweight: 25–29.9
  •  Obesity: BMI of 30 or greater

To calculate your BMI: divide your weight (in kilograms) by your height (in metres squared). For example if you are 1.78m tall and weigh 67kg it would be 67kg/(1.78×1.78) which equals a BMI of 21.

What are your options?

If your BMI is not in the normal range it is wise to try and make some changes to your lifestyle that will positively impact your weight. The “business” of daily life makes it difficult for many of us to maintain a healthy weight, but it is possible to lose (or gain if required) weight and get in better shape if you adopt a healthy plan. Here are some tips for getting to an ideal BMI:

  • Determine your BMI: Do your BMI calculation and determine what category you fall into.
  • Have a goal: If you plan to lose weight do it gradually. Losing weight too quickly might seem like a good idea, but most people tend to regain the weight that they lose too quickly. Often a goal of losing 5 to 10 percent of your weight over a six month period is a good starting point. Use a health and fitness app to track your progress if that helps.
  • Exercise: Regular, moderate intensity exercise helps to maintain a healthy weight, and has many additional health benefits including reduced stress levels and better sleep patterns. Aim to exercise most days of the week for at least 30 minutes.
  • Eat heathy and within your range: Eat a healthy balanced diet and eat within your recommended kilojoule intake. Remember that if you are aiming to lose weight your energy out must exceed your energy in.
  • Seek help if required: Talk to your doctor or consult a dietician if you are seriously overweight before commencing a major diet or exercise program.
  • For those who are underweight: If you are underweight, you might be exercising too much and/or not eating well enough. Modify your exercise program and make sure you eat a healthy, balanced diet.


Watch Dr Pooi Leng Lee’s video for further advice.

Please note: This video may not be copied or used, in whole or in part, without the prior written permission of City Fertility Centre © 2017.


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