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What Affects Birth & Fertility Rates?

Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

Did you know that there 4.3 babies are born every second around the world? That's is a lot of babies! However, some countries would like to lower fertility and birth rates while others would like to increase these rates. In this lesson, learn what affects birth and fertility rates around the world.

Global Population

7.4 BILLION people! That's an estimate of the global population as of 2015. About 90 million of those people were born during 2015. With approximately 350,000 births daily, that's around 255 births per minute! Amazing isn't it? So, you might think that with that kind of birth rate our population would be increasing quickly, but, actually, the average birth rate, especially in developed countries such as the United States has declined over the past few decades.

Fertility vs Birth Rate

So what is behind these changes in our population growth? Well there are lots of factors -- social, economic, religious, medical, etc. But let's start with a few key terms. The simplest term to start with is birth rate. This calculation is the total number of births divided by the total number of people in that population, including men, women and children. This is then multiplied by 1000. So. . . if we have 400,000 births in PA, and we have 700,000 residents of PA the birth rate would be:

(400,000 / 700,000) * 1000 = 571 births for every 1000 people in PA.

We can compare birth rate to the death rate (number of deaths in a population) to see how quickly the population is growing. If the birth rate exceeds death rate then our population is growing. If it is below the death rate then the population is not growing.

But we also have other ways of looking at population growth. To more accurately get a sense of how many women are reproducing in a population we can look at a fertility rate. Similar to birth rate the general fertility rate is calculated per 1000 people. But in this case those people are only women, ages 15-44. Why those ages? Because that is the average reproductive lifespan of a female, the time during a woman's life in which most children are born. So back to our PA example. We still have 400,000 births but now our rate is calculated using only women, ages 15-44. So say that number is 500,000. Now our general fertility rate would be calculated as follows:

(400,000 / 500,000) * 1000 = 800 births per 1000 women ages 15-44.

But sometimes these large numbers can get confusing so we can also calculate the TFR. This calculation gives us the average number of children, per woman in a given population. This is calculated regardless of age. This calculate is a little more complicated to do so we won't get into that but we can explain the results. If PA has a TFR of 2 that would mean that, on average, there are 2 children for every woman in PA.

This number is important because in order for a population to stay stable, the total fertility rate needs to be 2.1 or higher. Meaning, on average, there are 2.1 children born for every female during her lifetime. Those 2 children essentially replace their mother and father when they pass on, keeping the population stable. If the TFR was 3 then the population would grow, if the TFR was 1 then the population would decline. In 2014, the rate for the USA was 1.86, too low for population growth.

Estimates of average fertility rates around the world. Colors represent average TFR, or number of children per women.
World Fertility Rates

Reasons for Decline

One of the reasons for the decline is that developed countries, such as the USA, have more access to education for women, meaning more women are entering the workforce and delaying or forgoing having children until they have reached a stable position in their career. Many women in the workforce have less children than women who choose to stay at home. Increased education also means increased knowledge of birth control methods, giving women more control over when or if they have children. Research indicates that women in developed countries with less education have 2 times as many children as those with higher education.

The number of women entering the workforce has been increasing over the past few decades
Women in the workforce

In developed countries, more people also live in or near cities. Such urbanization means that families don't have as much space as those in suburban or rural areas. They also have less need of children to help 'run the family farm' or do essential tasks. This also leads to families have less children.

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