This is just a quick pulling together of Canada vs New Zealand vs The Untied States crude birth rate records for 1940 to 1960. Total population birth rate for the USA and NZ was used to match the Canadian total birth rate, so no regard is being made for population ethnic variation.

#vital statistics of the United States 1940-64
#http://www.cdc.gov/nchs/data/vsus/vsrates1940_60.pdf, Table 10 page 114
#for 1959 and early using births adjusted for underreporting
usaTotalBR <- "
year,rate
1960, 23.7
1959, 24.3
1958, 24.6
1957, 25.3
1956, 25.2
1955, 25
1954, 25.3
1953, 25.1
1952, 26.1
1951, 24.9
1950, 24.1
1949, 24.6
1948, 24.9
1947, 26.6
1946, 24.1
1945, 20.4
1944, 21.2
1943, 22.7
1942, 22.2
1941, 20.3
1940, 19.4"

usaBR <- read.csv(text=usaTotalBR)

#statistics canada
#Table B1-14
#Live births, crude birth rate, age-specific fertility rates, 
#gross reproduction rate and percentage of births in hospital, Canada, 1921 to 1974
# http://www.statcan.gc.ca/access_acces/archive.action?l=eng&loc=B1_14-eng.csv

canurl <- "http://www.statcan.gc.ca/pub/11-516-x/sectionb/B1_14-eng.csv"
canBR <- read.csv(canurl, skip=28, stringsAsFactors = FALSE, header=FALSE, nrows=25)
canBR <- canBR[!(is.na(canBR$V2)),c(2,9)]
names(canBR) <- c("year", "rate")


#Statistics New Zealand http://www.stats.govt.nz/infoshare , downloaded Population Crude Birth Rate (Maori and total population (Annual-Dec) 1872-2014 for the Total Population)
nzBR <- read.csv("DFM334304_20151107_015657_62.csv", skip=70, stringsAsFactors = FALSE, header=FALSE, nrows=21)
names(nzBR) <- c("year", "rate")

plot(usaBR$year, usaBR$rate, ylim=c(0,30), xlab="year", ylab="crude birth rate", main="crude birth rate\nbirths per thousand pop.", type="l", col="blue", frame.plot=F)
lines(canBR$year, canBR$rate, col="red", lty=6)
lines(nzBR$year, nzBR$rate, col="black", lty=2)
text(1958,29,"Canada", cex=0.6, col="red")
text(1955,24,"United States", cex=0.6, col="blue")
text(1955,27,"New Zealand", cex=0.6, col="black")