Stats NZ insight analyst Rebekah Hennessey said there has been no sign of a post-lockdown baby boom.
"Most babies born in December and January are the ones that would have been conceived during the lockdown time.
"Most of them are registered in January and February and we actually had a decrease in the number registered in that quarter than in the previous year, or even several years before that."
In spite of suggestions of a Covid lockdown baby boom, Hennessey said the findings fitted with previous data during times of crisis.
"A lot of the research has shown that when there's that economic uncertainty and other things going on, you do get a decrease in the number of births.
"So we haven't really been surprised but I was interested to see what it would do because you do hear a lot of stories either way."
She said the drop in registered births over Covid was reflected in most other countries with published data, and there were a number of reasons for the decline.
"I think the financial side of it is probably a big part," she said.
"Also the uncertainty around some of the social aspects, like thinking will I be able to have my family to come over and help, or anything like that."
The total fertility rates for the March year were at an all-time low of 1.6, down from 1.61 in December, Hennessey said.
And a post-Covid baby boom can't necessarily be expected in the coming years, as women were simply choosing to have fewer children.
"I suspect that the fertility rate will probably stay relatively stable for a while," she said.
"Certainly for the projections, we've got it staying relatively stable for the next 25 years.
"For the projections we've got the fertility rate staying at 1.65 which is at the lower end but I think that just shows that fewer women are having children at the moment.
"I'm not expecting us to see a sudden increase."
The effects of the pandemic could also be seen in declining death rates. In the year ended March 2021, there were 32,907 deaths registered in New Zealand, compared to 34,518 in the previous year.
Factors such as improved hygiene practices in light of Covid may account for this change, Hennessey said.