What weight should you be to get pregnant?

You hear it often, but I have to say it again: your weight is a major factor affecting your fertility and pregnancy outcomes.

When you are about to embark on a new pregnancy, your body does an audit. You could compare it to a financial assessment of starting a major construction project. It’s about evaluating the risk as well as available resources.

Your body’s resources are what you don’t use immediately, the storage of glycogen and fat among other nutrients.

When some women don’t have enough body fat, they will struggle to produce healthy levels of hormones for pregnancy. This can get so bad that you will stop ovulating and having periods.

But what happens if your weight is too high?

We may argue that the body’s resources are abundant, but with excess fat you may face other fertility challenges.

Being overweight taxes your body. You may be using your energy for fighting chronic conditions associated with higher weight like inflammation, sleep deprivation, pain, high blood pressure, dysregulated reproduction (HPO) axis. In short, the resources you need to fall pregnant, you use up for managing chronic conditions.

No two overweight women are the same. One will fall pregnant easily and the other will struggle.

One of these women has a healthier diet, controls her weight, and exercises. While the other eats fast food and sits on the couch. It’s like one of them is putting money in the bank each month and the other is drawing down. And even if at a given moment, their account balance may look similar, the risk assessment and prognosis you can do in each situation is desperate.

This is the reason, when considering a fertility diet, the first element we need to discuss is your weight.

Calculate your BMI here.

What does your BMI say about chances to conceive?

If your BMI is

  • below 18.5 you are underweight,
  • between 18.5 and 24.9 is normal, healthy
  • above 25 you are overweight, and
  • Over 30 falls into the obese category.

However, keep in mind that BMI is just an indication. The are weaknesses:

  • Body mass index, it doesn’t show your actual fat mass. Your BMI could be within the normal range, but you could store unhealthy amounts of fat. Or opposite, you can have a high BMI, but a healthy fat mass.
  • Does your body store fat abdominally?  This is also a factor. BMI does not reflect this.

Despite this, most research articles commonly use BMI to describe the relationship between weight and your chances to fall pregnant. For this reason here, we are going to use BMI as a weight indicator. This must be viewed in the context of your general health and lifestyle.

How does your weight affect fertility?

Body fat, as such, is not bad for us. The key is having a healthy amount of it. Fat acts as energy storage. But more importantly for fertility, it helps to regulate reproductive hormones and ovulation.

Girls at puberty need to reach 17% of body fat to start menstruating. However, 17% of body fat is insufficient to keep the periods regular. For the reproductive axis to run smoothly BMI has to increase and fat has to reach 22% of body weight. 

Underweight

Being underweight, reduces uterine receptivity, increases time to conception and increases the risk of miscarriage. 

Reduced uterine receptivity

Women make oestrogen in both their fat cells and ovaries. To ovulate and have healthy periods, healthy amounts of oestrogen from both sources are required. That’s why being underweight, or with less than 17% body fat, can compromise ovulation and stop periods altogether. 

As little as a 2% reduction from healthy fat levels can be enough for your cycles to be irregular.

Takes longer to fall pregnant

It takes four times longer to fall pregnant when you are underweight. As discussed, some of the reasons for this may be low levels of hormones, fewer ovulatory cycles, and lower uterine receptivity. 

Miscarriage

Very lean women make weaker forms of oestrogen. This, in turn, affects the uterus’ ability to host the embryo. This may be one of the reasons why women with a low BMI are 72% more likely to suffer a miscarriage in the first three months.

Overweight

Excess weight may lead to compromised ovulation, reduced uterine receptivity, and miscarriage. Furthermore, it may affect the chances of getting pregnant with IVF. Pregnancy complications are also more common. This includes high blood pressure, diabetes, low/high birth weight, and more complicated labours. 

Increased inflammation

Unhealthy amounts of fat, especially around internal organs, may create low-grade inflammation in the body. The biggest danger occurs when fat cells balloon in size and start to ooze inflammatory proteins—known as cytokines—into your bloodstream. Cytokines reach your ovaries and uterus, spreading inflammation. Inflammation can affect ovulation, hormone production, and uterine receptivity, reducing the chances to conceive. 

Anovulation

Excessive body fat may interfere with the mechanism of ovulation. For example, women with a BMI above 27 are three times more likely to have non-ovulatory cycles. Less frequent ovulation equals fewer chances to fall pregnant.

Miscarriage

Obesity may cause chronic inflammation. Increased inflammatory markers have been shown to affect ovarian health. In particular, healthy egg development. Obesity can also compromise endometrial receptivity. These could be the reasons why women who are overweight are more likely to miscarry.

Reduced success rate with IVF

Unfortunately, IVF can’t undo the damage caused by excess weight. On average, obese women’s chance of having success with IVF reduces by 20% (live birth rate). And being overweight reduces the chance by 9%. 

High BMI may lower IVF success rates because increased body fat can disregulate hormones and disrupt the health of the endometrium. These changes affect all aspects of fertility from egg quality, fertilisation to implantation and the risk of miscarriage. 

Excess weight will affect pregnancy and the health of future children

Maintaining a healthy weight is equally important during pregnancy. Excess weight during pregnancy may affect your child’s ability to have babies. Additionally, it increases their risk of developing diabetes and heart disease. Researchers found that for every kilo of excess weight women had pre-pregnancy, it increased the risk by 4.5% of their child becoming obese.

The health of the mother during pregnancy affects not only the child but even future generations. A good example of this is a study published in 2020

Researchers discovered, that the grandchildren of women who had no excess gestational weight gain were less likely to be overweight or obese in adolescence and when they were adults.

Not to mention that being overweight during pregnancy increases risks for gestational diabetes, high blood pressure, and preeclampsia.

The good news: overweight women who follow reduced-calorie diets and do exercise are more likely to lose weight, start ovulating, and fall pregnant. Some studies show that weight loss increases the chances of natural conception pre-IVF.

What insulin resistance does to your fertility?

Insulin resistance affects all key fertility events—ovulation, fertilisation, and embryo implantation. It also affects sperm quality. Sadly, it can even cause first trimester miscarriages and infertility.

Insulin resistance wrecks havoc on your ovaries

Insulin is a hormone. Ovaries are covered with insulin receptors. Healthy insulin levels are essential to ovarian health. 

High circulating levels of insulin and lipids (fat) will affect your other reproductive hormones, consequently, delaying or even suppressing ovulation. This can lead to irregular cycles. A classic example of the effect of insulin resistance on ovaries is PCOS. 

Accelerates ovarian ageing

More advanced insulin resistance may lead to Type 2 diabetes. Uncontrolled Type 2 diabetes can cause small blood vessel damage in your ovaries. This is bound to reduce healthy ovarian blood circulation. Reduced blood flow is a feature of ageing ovaries, and is likely one of the reasons for declining egg quality. 

As a result of the damaging effects of insulin resistance, women with Type 2 diabetes are more likely to enter menopause earlier.

Increases risk of miscarriage

Research has linked insulin resistance with an increased risk of early miscarriage. And women who had three or more pregnancy losses are likely to have insulin resistance diagnoses. 

Insulin resistance on sperm quality

 In conclusion, insulin resistance in men with unexplained infertility may be a cause of reproductive and metabolic abnormalities. The benefit of insulin-sensitizing agents for these patients should be explored. 

Insulin resistance and IVF 

Insulin resistance is also a hurdle when trying IVF. Studies show that IVF isn’t enough to  avoid the harm caused by insulin resistance. Consequently, women with insulin resistance are more likely to lose pregnancy after IVF treatments. Miscarriage is a traumatic experience. And it is especially distressing for women who achieve pregnancy through the highly invasive, expensive, and stressful treatments. 

Another important aspect, IVF patients with insulin resistance may require higher doses of gonadotropins and have a higher risk of developing gestational diabetes.

 

PCOS

Can insulin resistance cause PCOS? Can PCOS lead to insulin resistance? We don’t know. 

Either way, the majority of women with PCOS will experience some degree of insulin resistance. The bodies of women with PCOS can make insulin but can’t use it effectively. Excess insulin tells the ovaries to make more testosterone. Insulin and testosterone fuel each other’s production.

Excess testosterone and insulin aggravate PCOS symptoms and compromise fertility: 

How to optimise your fertility by breaking the cycle of insulin resistance

We need to figure out the best way for each person to break the insulin resistance cycle. 

As you can see from the paragraphs above, healthy insulin levels are essential when trying to conceive. Additionally, insulin resistance and its harmful effects can be passed onto future generations. Impaired glucose tolerance in mothers has been linked to insulin resistance in babies

 

To sum up, the lifestyle changes you are going to make today:

  • Can help you to fall and stay pregnant,
  • Will improve the health of your future children,
  • Optimising your health before pregnancy will reduce the risk of your kids having difficulties making babies.