The Social Democrats, Greens and Left Party scored a combined total of 48.5 percent, while the Moderates, Liberals, Centre Party and Christian Democrats received the support of 45 percent of those polled.
"Historically, statistics have shown that the bloc leading in April also tends to win the election. That has happened eleven times out of thirteen. Those are the statistics the government has to beat," Sören Holmberg, professor of political science at Gothenburg University, told Svenska Dagbladet.
With 4.9 percent of respondents pledging their support to the Sweden Democrats, the far-right nationalist party would hold the balance of power in the Swedish parliament if an election were to be held today.
All changes recorded since March were within the margin of error, with the Green Party recording the biggest swing, down 1.6 points.
"My main commentary is that things are very stable. Hardly anything has happened," said Sören Holmberg.
April poll results, Sifo (change since March in parentheses)
Moderate Party 29.8 (-1.0)
Centre Party 4.9 (+0.2)
Liberal Party 6.2 (+0.3)
Chrisitian Democrats 4.1 (+0.3)
Centre-right coalition: 45.0 (-0.2)
Social Democrats 34.1 (+0.1)
Left Party 5.4 (-0.2)
Green Party 9.0 (-1.6)
Left-green opposition: 48.5 (-1.7)
Sweden Democrats 4.9 (+1.1)
Others 1.6 (+0.7)