https://ourworldindata.org/fertility-rate
If you do ctrl+f and go to 'Birth Rates Around the World' and change the plotted countries to East/West Germany, you'll find that both countries have a similar trend line, apart from 1954, where East's birth rate increased by around 30 kids per thousand people. It's such a dramatic spike, but I don't understand why?
At first I thought perhaps celebrating the 1954 world cup won by Germany, but I doubt it as it was in the same year as the demography change, and West Germany did not see a spike.
I think that dramatic spike is a data error - at some point, a "1" became a "4." The chart shows the following data for East Germany from 1952-1956:
The source isn't listed - the site simply says that the information came "from many primary sources including official national statistics and international abstracts dating back to 1750."
The German Federal Statistical Office (Statistisches Bundesamt) keeps the numbers on topics like this. They refer to the former GDR in their statistics as "New Federal States and East Berlin" ("Neue Länder und Berlin-Ost"). Finding their numbers on this topic requires the Internet Archive, but if you look at p. 7 of this PDF, it's all there. Column 2 (Lebendgeborene je 1 000 Einwohner und 1 Jahr, "Living Births Per 1,000 Inhabitants Per Year") shows that the birthrate in the GDR in 1954 was 16.3 births per 1,000 people.