You are going to hear a lot about population in the coming week. That's because on 31st October, the United Nations Population Fund will announce that the number of people on the planet has reached seven billion.
Of course no one knows exactly how many people there are - we may have already passed seven billion - but the UN has picked the day as the best estimate.
I've been to Zambia because it has one of the world's fastest growing populations.
I have been to many maternity wards around the world but never one as busy at the United Teaching Hospital (UTH) in Lusaka.
They deliver at least 50 babies a day - sometimes 70 or more. The pressure on the maternity unit is significant according to Dr Lackson Kasonga.
"The population is expanding rapidly, especially in the capital where people are moving for jobs. The demand for maternity services is rising each year but that is not matched by the increase in space or resources."
Women in Zambia have, on average, six children. That number has barely shifted in recent decades. Contrast that with global fertility, which has fallen from five to two and a half children since 1950.
Catherine Phiri had just given birth to a daughter when I met her and husband Robert. They have two boys at home. A fourth child died in infancy. They live in poverty, like two-thirds of Zambia's population. The Phiris want more children and, like parents the world over, they are ambitious for their future.
Catherine Phiri told me: "I want my daughter and my sons to be important people in government so as they work they can extend help to us. We grew up suffering and I want it to be different for them."
Although basic education is free, there is often pressure to get older children to begin work so that they can help with the family finances. Robert Phiri said: "We'd like five or six children but I worry if we are going to be able to send them all to school. If we have more it might mean some going to school and some not - we will have to see what happens."
I visited the family home outside Lusaka. It is extremely basic. There is electricity but no running water. Mr Phiri earns below the minimum wage and the couple often don't have enough money to buy clothes.
I asked Anna Sampa from Unicef why so many poor couples in Africa choose to have large families. It's something that I have found on visits to Sierra Leone, Malawi and other developing nations.
She said: "They don't see the potential burden of having more mouths to feed. Rather they look on lots of children as a means of helping them in their old age."Aid agencies do not talk about population control - they fear it smacks of eugenics. Rather, they try to encourage family spacing and getting couples to have the number of children they can support.
At UTH I watched a demonstration on contraceptive methods given to a group of pregnant women. The majority of couples in Zambia still don't use modern methods such as condoms, the pill, implants and injections.
Even though contraception is free, many women can't afford to travel to the health centres. There is also a good deal of ignorance about the methods available according to Ruth Bweupe, family planning officer at the Ministry of Health.
"The myth surrounding the implant is that it will go to the heart or the brain and do serious harm. The implant rods are inserted in the upper arm so they feel that it will travel around the body. For the pill they feel it will cause permanent infertility and they'll never be able to have children again."
The rising workload of UTH's maternity unit is a tangible sign of Zambia's growing population. It is 13 million now and projected to triple by 2050 according to the UN Population Division. Even its most cautious projection has the population at 100 million by 2100, with its medium (or best estimate) being 140 million.
Does that matter? After all, Zambia is a big country, three times the size of the UK. It has fertile soil and rich mining reserves, so there is huge potential.
The economy is growing and the World Bank recently re-classified it as a "middle income" country. How this works given that two-thirds of families live in poverty is a little baffling, but it is an indicator that Zambia is improving economically.
Despite the heavy workload at the maternity unit, Dr Kasonga was upbeat about the future.
"We are happy to have more babies. This is a vast land, so we need more people. But it is the speed which is the cause for concern - we need to match population growth with resources."
Half of Zambia's population is aged 16 or under and it has a relatively smaller elderly population. Contrast that with most developed countries where the problem is that fewer and fewer people are supporting a growing cohort of elderly.
The potential problem for Zambia is that the population increase is so rapid that the government may struggle to keep pace. Those under 16 need education, healthcare and homes but they are not yet contributing to the economy. Zambia can barely feed 13 million people so how will it cope in the future?
Part of the answer will depend on how Zambia manages and encourages foreign investment - China is a huge player here. It also depends on the life chances given to the young, which starts with education.
Unicef supports education projects in Zambia and believes empowering women is vital if couples are to be lifted out of poverty and have the number of children they can support.
At Munali High School in Lusaka, most of the teenage girls I spoke to came from large families. But all wanted careers first and motherhood second. Their attitudes seem a world away from the older generation.
Norah Zulu, who is 16, told me things were very different from her parents' day: "They never learned about family spacing. We do. And they did not have gender equality - rights for girls and boys. I want two kids, no more."
Mercy Mushindu, who is 17 and one of eight children, said she also wants two kids "to reduce the population".Things are changing in Zambia and it will be the next generation who will have to ensure that population increase is a benefit rather than a burden.