Birth Interval Trajectories during Fertility Transition in India, 1992–2021: Socio-Demographic Correlates and Regional Heterogeneity

In the story of human populations, two things usually happen together: families get smaller, and the time between having children gets longer. When a country moves from having many children to having fewer, it is often because parents are better able to plan when to start a family and how far apart to space their children. This spacing is not just a matter of convenience; it is a vital health factor. Medical science has long established that if a mother has another baby too soon after a previous one—specifically, less than two years later—both she and her children face higher risks of illness and death. Conversely, waiting a bit longer, ideally between two and three years, gives the mother's body time to recover and allows the older child to grow stronger. For decades, demographers have watched India, a nation of over a billion people, as it underwent a massive shift in family size. The expectation was that as the number of children per woman dropped, the time between births would naturally stretch out, creating a healthier environment for everyone.

Researchers from RMIT University and the International Institute for Population Sciences decided to look closely at this expectation using data collected over nearly thirty years. They gathered information from five different national surveys conducted between 1992 and 2021, tracking the lives of hundreds of thousands of women. Their goal was to see if India's success in reducing the total number of children born had also succeeded in improving the timing of those births. They found a surprising disconnect. While the average number of children per woman fell dramatically from 3.4 to 2.0, the time between births barely changed, increasing by only a single month over three decades. The study reveals that India's family planning efforts have been highly effective at stopping families from having more children, but they have been less successful at helping families wait the right amount of time between the children they do have.

The researchers discovered that this lack of improvement in spacing is not happening evenly across the country. In the southern, western, and northeastern parts of India, the time between births has lengthened significantly, with some states seeing increases of over thirty percent. However, in the central and northern regions, which are home to many of the country's most populous states, the time between births has either stayed the same or actually gotten shorter. This means that the national average, which shows a tiny improvement, is hiding a much more complex reality where some regions are moving forward while others are stagnating or moving backward. The data shows that about one in four births still happens within two years of the previous one, a rate that remains stubbornly high despite the overall drop in family size.

A major reason for this pattern lies in how family planning has been practiced in India for decades. The national program has focused heavily on permanent methods, specifically sterilization, to limit the total number of children a family has. While this approach successfully reduced the total number of births, it did not provide the tools needed to space them out. Sterilization is a final step; it stops the family from growing, but it does not help a mother decide to wait two or three years before her next child. The study suggests that because the system prioritized "stopping" over "spacing," many women who wanted to limit their family size did so quickly, often having their last few children in rapid succession. This is particularly true for families who already have two children and want to stop there; they may rush to have that second child and then stop, rather than waiting a long time between the first and second.

The researchers also looked at how factors like education and wealth influence the time between births, and the results were more complicated than expected. Usually, one might assume that wealthier and more educated families would naturally wait longer between children. However, the study found that the relationship is not a straight line. For instance, the wealthiest families sometimes had shorter gaps between births than middle-income families. The researchers suggest this happens because women in wealthier families often start having children later in life. Because they start later, they may feel a need to have their desired number of children in a shorter window of time, leading them to compress the spacing between births. Similarly, while education helps, the study found that only secondary education made a significant difference in lengthening the time between births, while primary education did not. This indicates that simply having some schooling is not enough to change these deep-seated patterns of family planning.

Regional differences played a massive role in these findings. The southern states of India, which have historically had better access to health services and lower rates of child marriage, showed the most improvement in spacing. In contrast, states in the central and northern heartlands, where cultural preferences for larger families and specific gender preferences for sons are stronger, saw little to no improvement. In some of these lagging regions, the time between births actually decreased. This suggests that a single national policy cannot solve the problem. The factors driving how families plan their children vary so much from one state to another that a one-size-fits-all approach fails to address the specific needs of different communities. The study highlights that in some areas, the pressure to have a son or the lack of access to reversible birth control methods continues to drive families to have children close together.

Ultimately, the paper concludes that India's demographic transition is incomplete. The country has successfully reduced the number of children being born, but it has not yet achieved the healthier spacing that should accompany that reduction. This gap matters because short intervals between births continue to put mothers and children at risk. The researchers argue that to fix this, the focus of family planning must shift. Instead of just counting how many children a family has, programs need to help families plan when those children arrive. This means moving away from a heavy reliance on permanent sterilization and toward promoting reversible methods that allow women to control the timing of their pregnancies. It also means tailoring these efforts to specific regions, recognizing that a strategy that works in the south may not work in the central plains. Without this shift, the benefits of having fewer children will remain limited, and the health of mothers and children will continue to suffer from the risks of closely spaced pregnancies.